GOD, they were tired. Long-term tired. Give-up tired. Jake’s loud singing was drawing the eyes of everyone in the street to them.

"The cas-TLE! Cas-TLE! Casss-TLE!"

Audrey wasn’t enforcing his rigid behavioural programme properly any more. It wasn’t changing anything. She had even stopped forcing his medication into him. She was so tired.

Jake was 11 and didn’t sleep. He skulked around the house at night. He stood at the end of their bed for hours, staring at them. They had installed CCTV in their room and saw him do it. One morning they found a hammer at the end of the bed. When they watched the recording back they saw him practise-swing it at Audrey’s head and laugh to himself. They installed pressure alarms on Jake’s bed after that to wake them when he got up. Audrey knew it was coming to a head. She could feel it. They all could.

At the top of the hill a man in full Braveheart costume crossed in front of them, looking down at Jake’s loud singing. He had a blue Saltire flag painted on his face. Jake saw it and changed his shriek to "Blue-LOO-LOO-LOO". He sang in soprano. As they approached the Royal Mile his voice was increasingly amplified by the high tenements.

Trailing behind Jake were six-year-old Simon and seven-year-old Hannah. His little brother and sister kept their hands deep in their pockets, their heads down. Audrey and Pete followed up the rear, both shamefaced and thinking the same thing: they should have kept Jake on his medication. The pills made him fat and tearful, he wet the bed more than usual and that made it hard for them to go away anywhere. Audrey had to corner him and pinch his nose to make him open his mouth. She had to force him to take them. She didn’t know if she could manage his behavioural problems any more.

Years ago, when Jake had tried to drown Simon in a paddling pool and laughed when they told him off, Audrey’s mum had said: "He hasn’t got behavioural problems, he’s just a vicious little arsehole."

Audrey had sobbed at that. Her mum cuddled her and cried with her and said, "No, sweetheart, look, he’ll grow out of it. If someone doesn’t kill him first. Ha ha. Have you considered exorcism?"

Audrey stayed away from her mum now. Jake didn’t need any more negativity around him. He got enough of that at school. He’d killed the class gerbil, he hurt other children if he was left alone with them. Play dates and parties always ended unceremoniously. Only Audrey saw how isolated Jake was, how vulnerable. He was desperate for friends. He didn’t care what age they were. He was always wandering off when they were shopping, following children or adults. He seemed terribly alone and it would only get worse. She knew that.

At the end of the road Jake saw the castle, threw his head back and ululated: "CASTLULULULULULUL!"

Their last faint hope was that Jake would grow out of it. He had been on different types of medication, seen psychologists, psychiatrists, ministers, been on behavioural boot camps. When he beat the neighbour’s dog to death with a brick two years ago, social work moved him to a different school. They wanted him to go to a residential facility. Pete was keen but Audrey couldn’t send him away. Their last and only hope was that he would grow out of it.

"CASTLULULULUUUUUU!" Jake’s eyes were protruding. He was shaking. He was going to blow.

It was a busy street. Everyone was looking at Jake. His body was rigid, his blue hoodie was drawn tight around his intensely red face. Tourists were watching him, not judging, just interested in the mad singing boy. They had no idea how bad things were about to get.

Hannah put her arm out to stop her little brother from walking into Jake’s clawing radius. She grabbed Simon’s green hood, pulled him back down the hill to a safe zone. She looked imploringly back to her parents.

Audrey hurried over and knelt down in front of Jake. He looked feral, 11 but small. His eyes were wide and blank. He couldn’t see her. She leaned in, filling his field of vision with her face, and held him firmly by the shoulders.

"Jake, I need you to calm down."

"CALM! CALMLULULULUL!" He ululated in her face. Spit flecked her eyelids.

"I need you to take a deep breath and caaaalm yourself down."

Audrey moved her hands to his upper arms and held him tight, ready for a secure hold if he went for her. "Breathe in and out, in and out. Do it with me." She breathed deeply, setting an example.

Sudden as a cat spotting a mouse, Jake focused on her face. "I fucking hate you, Mummy."

"That’s it, breathe in."

"I hate you."

"And out."

"I’ll bite you again." He looked at the scar he had gnawed on her chin.

Audrey was very, very angry but she blinked it back. Jake was being provocative to get a strong reaction. She would only have to act calm for a short while because it was Pete’s turn to drag him back to the hotel and guard him while he had a tantrum in a stimulation-free environment.

"You’re too excited." She spoke in a flat voice. "You’ve let yourself get too excited."

He glanced at the castle again and suddenly realised what "too excited" meant. He was going to be removed, denied the castle and the cake and the baked potato lunch. She steeled herself as Jake’s body tensed, he bared his teeth and bent his knees, ready to spring.

The shadow of Pete fell over them, hands out, in position to apply the hold they had been taught to use on him. Jake’s eyes flicked to his father and he flinched, knew his physical attack on his mother was foiled.

"When you’re asleep …" Jake growled. He saw the spark of alarm in her eyes and smiled.

This morning in the hotel Audrey had swung her feet over the side of the bed, stepping onto a jagged glass ashtray discarded on the floor. She hadn’t told Pete. It was terrifying. It was an escalation.

"I’ll do it," he snarled.

Something snapped inside of her, a cold wash over her heart. Eleven years of soul-grinding humiliation, of shame and blame, of confrontations about Jake’s behaviour. And tiredness. Everyone thought it was her fault. Maybe it was her fault. She had done her best. Her best was enough for Hannah and Simon but it wasn’t nearly enough for Jake. She couldn’t do this any more.

"Right," she said. "We’re going home."

Jake glanced desperately up to the castle. "To the hotel?"

"No. To Surrey. Remember Helen, the social worker? She’ll meet us there."

"Why Helen, Mummy?"

He was too old to call her that. It sounded facetious and strengthened her resolve.

"You need help." She squeezed his upper arms hard. "And I’ve tried but I can’t seem to help you. I’m finished."

Never confront him, Pete had said, nursing a bloody cut on his forehead. Audrey didn’t care any more. She shut her eyes, expecting him to start clawing at her, at her eyes, at her lips.

But Jake didn’t. He looked at her, expressionless, unblinking, and spoke in an unfamiliar voice: "I’m finished too."

It was a normal voice, not strangled or grating. Not the voice that made strangers in the street want to slap him. "I’m finished too, Mum."

"You’ve finished what?" she whispered.

"This behaviour. It’s finished." He looked at the castle battlements then back at her. He held her eye.

Pete hadn’t heard this. When he spoke his voice sounded high and frightened: "We popping back to the hotel for a time out, Jakey?"

Audrey released her grip slowly but Jake didn’t move. Hannah and Simon backed away. But Jake didn’t go for anyone. Uncertain, Audrey stepped away.

Jake smiled up at her, a warm smile, and his eyebrows tented in a question. He looked up the winding lane to the castle and back at her for permission.

Reckless with exhaustion, Audrey raised an arm to the castle. He trotted away along the pavement.

Hannah and Simon watched their brother run off by himself. Hannah chewed her cuff. She did that when she was scared. Little Simon was baffled by the lack of drama and looked anxiously to his father for reassurance. Pete ruffled Simon’s hair and watched Jake walk calmly away. He looked at Audrey. She shrugged that she didn’t know what was going on either.

"He said he was finished with his ‘behaviour’."

"What, the ululating?" asked Pete.

They watched him walk away, dazed by the change in his mood.

"I don’t know what he meant."

Jake glanced back, saw they weren’t 20 feet behind – he had been warned about staying a safe distance to the group – and stopped. He waited. Audrey couldn’t believe it.

"Okay," said Pete, tentative but hopeful. "It’s a castle. There probably isn’t that much he can break." He swung Simon onto his shoulders. "Come on then. Let’s just see how it goes."

Audrey was cautious but she was desperate enough to hope.

It was an extraordinary hour.

They took in the views of the hills from the wide esplanade leading up to the castle. They queued for cartons of juice from a van. They had to wait because a man in front of them had ordered an elaborate coffee but Jake didn’t go crazy. He didn’t get frustrated with the lady serving or throw all the food out of the baskets at the front of the van.

They walked together. Jake didn’t run or shout. He didn’t walk ahead of the group or pester his siblings. He didn’t demand Simon’s place on his dad’s shoulders. He was calm, even cheerful sometimes. He kept trying to get Simon to pull his green hoodie up like him and pull it tight around his face. Eventually Simon did and they laughed together because they both looked bonkers. Usually any concession to a demand by Jake just prompted him to make more and more and more demands but he didn’t do that this time. He just touched his little brother fondly on the hood and let him alone.

It was exposed on the castle forecourt. A bitter wind picked up and the sky darkened as they approached the entrance. A little wooden bridge over a 20-foot sheer drop led to the Portcullis Gate. They were standing near one of the official guides to the castle, an older man wearing the red anorak uniform, with a walkie-talkie clipped to his shoulder. Pete asked him who the statues were on either side of the Portcullis Gate. The guide explained that they were William Wallace and someone else. Audrey wasn’t listening. She was watching Jake. He was listening to the man, reacting appropriately, nodding to show he understood. It was remarkable. Apparently he could behave when he wanted to. She was delighted and furious in equal parts.

Pete snapped pictures on his phone and the guide offered to take a family photo. They gathered dutifully and the guide took it and gave the phone back to Pete. He showed it to Audrey. They all looked surprised, except Jake. He was in front of the rest of them, smiling straight to the camera.

Pushing their luck, Pete asked what the Latin inscription over the Portcullis Gate meant. "Nemo me impune lacessit," said the guide, "means 'cross me and suffer'." He giggled, a high-pitched and contagious laugh: "Oh! It’s not very friendly, is it?" He laughed again.

Simon caught Jake’s eye and they laughed together. Audrey couldn’t remember that happening, not since Simon was a baby. He knew better than to catch Jake’s eye now.

Pete was happy and excited. "Okay gang, let’s go and see this castle!"

Audrey watched him lead the boys up a steep cobbled lane. Hannah hung back with her mother. She was unsure of New Jake, less willing to trust. She chewed her cuff, keeping her watchful eyes on Jake.

Audrey took Hannah’s free hand: "Okay, honey?"

Hannah smiled up at her mum but her eyes were scared.

"What is it, sweetie?"

"What’s – " She glanced at Jake and stopped. Hannah didn’t talk much. The school had highlighted her "virtual selective muteness" as a cause for concern. Audrey filled in for her, a habit the school had warned her against. "What is happening with Jake?"

"Hmmm."

"I think he’s trying to be good."

Hannah gave her mother a sceptical look. Audrey nodded, "I know but look how happy Daddy is. We’ll see. Let’s try to have fun while we can, okay?"

Hannah nodded, keeping her reservations to herself. She had been through so much, suffered because of Jake’s behaviour. She was so brave about it. Audrey said: "You’re lovely, Hannah, d’you know that?"

Delighted, Hannah blushed at her shoes and squeezed her mum’s hand.

Before Jake got really bad a family counsellor told Audrey and Pete that they simply weren’t giving Jake enough positive reinforcement for good behaviour. She was wrong; they did it all the time. They complimented him for anything that wasn’t spiteful or vile. He never responded to compliments the way Hannah and Simon did. He didn’t really seem to care what they thought.

Wind buffeted them in the steep-walled lane. They stepped out of the blustery current, into an exposed yard and a battlement wall where a cannon overlooked the city. It fired at one o’clock every day. Simon and Jake ran over to it.

Magnificent views looked out over the north of the city across to a glittering strip of sea.

A different guide in the familiar red anorak was giving the history of the western defences to a Chinese tour group. Pete and Audrey and the three kids loitered nearby, listening in.

The castle was being besieged by Jacobites, announced the Guide. Some of the soldiers inside were sympathetic to the rebel cause and conspired to let in the besieging army. But they were caught. They were hung from these very walls by their own coats, left to rot there as a warning to others.

The tour group took turns looking over the wall, cooing, gasping, giggling with fright. Simon and Jake and Pete looked over the edge. Simon screamed. Jake laughed at him and Simon took it in good part. Audrey looked over and felt her stomach jolt at the 60-foot vertiginous drop to jagged black cliffs below.

Hannah stayed well back, giggled into her cuff and shook her head when Audrey pretended she would make her look.

When they were safely 20 feet away Simon did a little leap sideways towards the wall, pretending he was jumping over, showing off to Jake. Jake threw his head back and laughed. Simon was delighted at his brother’s approval. He loved Jake so much but it had never been safe to show it before.

They walked on, Simon pretending to jump over every wall they came to. He wore the joke out, he was only little, but Jake was kind about it and grinned when prompted.

They stopped for a cake and the boys sat together. Jake pretended his ginger cake was jumping off the battlements. Simon was thrilled that Jake was copying him. He was so happy he actually glowed. With their hoodies over their heads, one blue, one green, they looked like mismatched twins. Only Hannah held back.

When they had finished their cakes, Jake asked to see some dungeons. They walked up to an exhibition about prisoners of war. Napoleonic prisoners had been held in these very vaults, the sign said. They were held here for years. Hammocks were strung up high on the walls and plaster models of prison loaves were nailed to wooden plates. The kids wandered around, touching things and looking, and Pete and Audrey finally got a minute to speak.

"What is he doing?" Audrey whispered.

"I don’t know," beamed Pete.

They watched the kids clamber onto a high bench. Simon and Jake pretended to eat the plaster loaf. It was chipped and worn but they were miming eating it as if it was delicious. Hannah sat apart from them, still watchful, but softening.

"Maybe he has just grown out of it?" said Pete.

The boys were getting down and Jake put his arms around little Simon’s chest and swung him easily to the floor. He tried to help Hannah too but she yanked her arm away and wouldn’t let him touch her.

Audrey hummed non-committally. Something felt wrong. Growing out of behavioural problems was gradual, she knew that. It would be fitful, would come and go, if it happened. She should tell Pete about the ashtray by the bed this morning but it would spoil his day. She’d tell him later.

Crown Square was the highest point in the castle, a small courtyard with buildings on each side. It was busy, the clock was creeping towards lunchtime. Tourists thronged in groups, talking loudly in many languages, queuing impatiently for the tea room and the toilets.

They had promised the kids a baked potato for lunch, their favourite, but they had just had a cake so they needed to wait for an hour or so. The least busy door led to the National War Memorial.

Pete led them up the circular steps to the open entrance.

It was a beautiful building. It had been a church, a munitions store and a barracks, but its insides had been scooped out and it was refurbished as a secular chapel. Across from the entrance was an apse with a steel shrine containing an honour roll of all those who had died in conflicts since 1914. High windows of fine stained glass gave the place a sombre, whispery atmosphere. The kids liked it because there was lots to see. They all walked down to the left, to the western transept and found the memorial to noncombatants. The kids were guessing at Latin translations to the regimental insignia. They were all calm and whispering appropriately. It was how Audrey had always hoped it could be.

She nodded to the Latin motto the kids were struggling with.

"What does it really say?" She whispered to Pete, who had a little Latin.

"Hmmm. 'If … you like … pina colada …'." He smothered a smile.

"Interesting." Audrey cupped her chin, playing the part of the interviewer: "And this second line here, what does that say?"

"Ah, something about enjoyment and rain. Just let me conjugate the verb 'to capture'."

They giggled, muffling their laughter, leaning into one another, snorting. Their foreheads touched, just briefly, but it felt like a kiss. They hadn’t laughed together for such a long time. Audrey and Pete looked at each other, here in this unexpected pocket of calm. He mouthed "You’re gorgeous, Audie" and she smiled and slapped his arm playfully. She looked up for the cause of all their worries.

Jake was gone.

Simon and Hannah were together, she chewing her cuff, he with his green hoodie pulled up and tight around his face, tracing names carved into marble with his finger. The War Memorial was crammed with people.

"Jake!"Audrey’s voice reverberated around the silent stone room. Every face turned to look at her, none of them Jake.

Pete grabbed Hannah and Simon by the shoulders and ploughed his way through the crowd to the door. Audrey followed in his wake.

From the top of the stairs they could see the entire courtyard, see the alleys and doors. Even at a gallop he couldn’t have gone far.

"STAY HERE!" Audrey shouted at Pete and the kids.

She ran diagonally across the courtyard, past David’s Tower and up to a wide battlement with a low wall.

No Jake.

A pack of French schoolchildren milled around her chatting, checking phones, waiting for someone. She ran over the wall and scanned back towards the Portcullis Gate.

No Jake.

Getting her bearings, she realised that there were lots of places to hide over at the other side of the castle. Loos and cafes and doorways. She bolted downhill, running over the lawn at the back of the War Memorial, scanning the thinning crowds for Jake’s blue hooded head. Nothing.

Down through a narrow lane, she elbowed her way through a tight group of Korean women. She could hear them calling indignant reproaches after her as she ran, back to the cafe where they had eaten their cakes. She kept thinking I am going to find him. I am going to find him. She ran the phrases over and over in her head like a mantra, as if she could will it true.

Down by the cannon where the Jacobite soldiers were hung. No sign.

In the cafe, no sign.

She sprinted down into another courtyard. No sign.

She checked all the toilets she passed, holding open the doors of the gents’ and shouting "Jake?" but nothing. Then she saw a Guide with his walkie-talkie crackling on his shoulder. She ran over to him.

"Help me!" She was out of breath, sounded rude. "Sorry, I’ve lost my son."

He nodded calmly, as if this happened all the time, and held his walkie-talkie up to his mouth. "What’s he wearing?"

"Blue hoodie top. Cotton, pale blue. Hood up, pulled tight around his face. He’s 11. He’s lost."

The Guide put out a call to all of his colleagues, giving them her description of Jake and the last place he was seen.

Audrey caught her breath and looked around. Walking towards her, trotting down through the narrow lane, was Pete. He was alone.

"THE KIDS?!"

"I saw Jake! On the corner! I left the kids with a Guide and ran but he disappeared. He’s still here!"

"Was he alone?"

"I don’t know. I caught a glimpse of his hood and turned to tell the Guide to watch the kids. I ran to the corner where he was but he was gone."

The Guide who had put out the call for Jake reassured her that no-one could leave the castle without passing two gates. If any child came that way they would stop them. They had CCTV everywhere as well. It would be all right.

He sounded so confident that Audrey covered her face and cried with relief. Peter held her shoulders. "Come on. We’ll find him."

Audrey was out of breath. She put her head between her knees and caught up with herself. A lady from the cafe brought her a glass of water. She thanked her and drank it. Her throat was terribly dry.

Finally she said: "Let’s go back. He might appear again." She wanted to see Hannah and Simon. She wanted to hold them.

Pete kept his arm around her shoulders as they walked back up the steep path. They were in the narrow, crowded alleyway when they heard the scream. Bare and animal, it was a cry of visceral panic. They ran back down.

The crowd in front of the cannon were arranged around a blonde woman. She was standing back from the wall, hands wide at her sides, her mouth open in shock. The Guide reached her and the woman screamed again, quieter this time, and pointed a shaking finger to the wall. The Guide went over and looked down. He staggered back. He stood still for a moment.

Moving very slowly, he lifted his hand across his chest and reached up to his walkie-talkie. He muttered something and then his head dropped to his chest.

Audrey broke away from Pete and ran to the edge, shoving through the startled crowd to look.

Jake. Broken on the cliffs below. She couldn’t scream. She couldn’t breathe. She couldn’t move. Finished. He was finished.

Pete was there. He looked and saw it too. Far down on a cliff ledge lay a tiny body. It was face down, the blue hood turning red, redness creeping through the blue was the only movement. Legs bent in wrong ways. Inaccessible from above and below.

Audrey staggered backwards and curled over her knees. She vomited acid chunks of cake.

The Guide had moved everyone back from the wall when a sudden flurry of movement heralded the arrival of more red anoraks and other men in black fleeces. The air crackled with radio messages, to and fro, fast voices. Pete was sitting on the ground, head dropped, hands resting on his knees. He looked drunk.

"I’ll get Han and Si …" Audrey backed away on rubber legs.

She turned and walked blind. No, she thought now. No. No. Nonononononono. No.

The tourists in Crown Square were oblivious to the tragedy unfolding below them. They moved in audio guide trances, slow, lazy, diffident. Audrey barged straight through them. She turned the corner to the National War Memorial and climbed the steps. When she saw the Guide’s face she knew he had heard. He was shocked. He stood to attention when he saw her.

He touched her shoulder, tilted his head, searched her face for eye contact. Audrey shook her head at the ground. "Can’t," she hissed. "I can’t."

He understood. She couldn’t feel this now. He stood straight, shoulders back and spoke very clearly. "What can I do for you?"

"My other children. Boy and girl. Here. Who are they with?"

He searched her face again. "With me. Their brother came and got them."

He had misunderstood.

She took a breath and said it again: "My daughter and son were left with a Guide while we looked for the boy in the blue hoodie."

He nodded. "They were left with me, ma’am. The wee laddie in the blue top with the hood all tied up tight, that wee fella’s came up and said they were to go with him. Ten minutes ago."

She couldn’t process that but the man was certain. "He was just himself, I made sure of that. The call just came that you couldn’t find him and a minute later his Dad spotted him and ran after him. Then he came back and said his Daddy said to bring the wee ones. They all went down that way." He pointed to David’s Tower: "I’m a father myself. I thought you’d be over the moon. He was bringing them to you."

Audrey ran as fast as she could down to Pete, to the crowd, to the shocked guides and the men in black who were lowering a thick black rope over the wall.

A stretcher and paramedic in a harness were preparing to go over. An ambulance was rumbling up the hill towards them.

"He came back," she said quietly. Pete looked up from the ground. "After you ran. He came back and said you’d sent him for Hannah and Simon. They left with him…"

The police sealed the castle. No-one was allowed to leave. The ambulance parked on the forecourt of the cafe, the doors propped open.

At first the other tourists were sympathetic. They thought it was a terrorist attack. They became angry when they realised it was about careless parenting and lost children. Tour organisers approached the cops and made their cases angrily: they had a flight to catch, a restaurant booking, tickets for other attractions. But no-one was allowed to leave.

The guides were kind. Chairs from the cafe appeared for Pete and Audrey. There was still no sign of Simon and Hannah. They asked them what sort of kids they were? Sensible? Nervous? Naughty? A complete search of the castle grounds was organised. The police were led by the guides to all the sneaky corners and hidden places.

Audrey and Pete sat side by side on chairs, upright, watching the black rope snaking over the wall. They couldn’t tell the police or the guides what might have happened. What could have happened. Who they were dealing with.

Men formed a tight circle around the rope and a pulley was fitted. They watched the rope tug and tighten. Jake was coming up.

Audrey stood up, legs so stiff with terror that she nearly fell over. Pete had to catch her.

They stood, watching the men crank the pulley, lifting the basket stretcher up to the battlement walls. The stretcher was for an adult. The slack little body barely half filled it. He was strapped in tight with neon yellow belts, turning pink from all the blood. He had a tiny neck brace on, his face covered in bloody cotton wool with a hole in the middle for the oxygen mask. His chest wasn’t moving.

Audrey could tell from 30 feet away.

So could Pete.

The blue hoodie was too long.

Her knees buckled. It wasn’t Jake in the stretcher. It was Simon with Jake’s top on. Pete didn’t catch her this time. She slipped slowly down to the ground as the red stretcher was placed into the ambulance. A shocked quiet fell over the crowd, as if they were all praying in their many languages, to their many gods.

Suddenly the police walkie-talkies crackled to life in a chorus: "A girl matching Hannah’s description has been found in David’s Tower. She’s been strangled with her own coat. Don’t tell the parents yet."

Too late. They could see Audrey and Pete had already heard.

Pete sank down next to Audrey on the ground. Crowds shrank away from the couple as if their sorrows were a stain, as if they were contagious.

In the silence Audrey could hear the wind, the rumble of the ambulance engine, Pete breathing, short despairing puffs.

A voice behind her, familiar, loud, pleased.

"I’m finished, Mummy."

Extracted from Bloody Scotland, an anthology of original crime fiction by leading Scottish writers (HES, £12.99). Denise Mina won the McIlvanney Prize this year for her latest book, The Long Drop (Harvill Secker, £12.99)