SANNY gets a wee buzz as they come around the bend and into sight of the place. He hasn’t been here since he was nine, before his dad went inside. It brings back how he felt when he first saw it. He had been picturing some gloomy grey fortress like Stirling or Edinburgh, both of which remind him a wee bit too much of the Bar-L now. He hadn’t been ready for the colour, for the redness rising out of the green, so bright and vivid even on a cloudy day.

It’s even more colourful this morning. As he predicted, the place is totally hoaching. There are dudes walking about dressed as knights and soldiers, jugglers in jester outfits, women in medieval dresses with their diddies spilling out. Of course, not everybody got the right memo. He also sees some blokes in flowing black robes, the material billowing around in the breeze, their faces covered in golden death-head masks. He recognises the get-up from thon film about Spartan warriors, the one starring that mad c**t fae Paisley. It’s not quite in keeping with the appropriate historical period or even geographical region, but then there’s weans dressed as Spider-Man and Power Rangers, wee lassies done up like her out of Frozen.

Most eye-catching is a replica siege tower. Essentially it’s like a giant ladder on wheels, with the platforms inside protected on three sides by wooden boards, and a hinged gangway at the top like a portable drawbridge. It’s swarming with weans, climbing all over it like wee monkeys, totally ignoring the shouts of their parents to get doon aff it or at least be careful.

“This is only a half-scale replica of the engine brought here by the English in 1301,” some tour-guide dude in a knight outfit is saying to a group of tourists. “In the thirteenth and fourteenth centuries, there was siege after siege, with the castle changing hands back and forth. The Scots had spent fourteen bloody and sapping months laying siege to the castle in 1298, only for the English to recapture it inside a month three years later with the aid of their mammoth siege tower known as The Belfry.”

Sanny catches Sid pure gawking at it. They share a grin, both thinking the same thing. Sid comes right oot with it, though.

“Just think of the places you could tan wi’ that.”

There is an archery demo going on to the right of the castle’s entrance, the area cordoned off for safety. There are two targets set up beneath the castle walls, a bloke holding a bow as he gives instructions to a group of teenagers. Sanny and Sid watch for a bit, taking in the portable frame where the spare bows are hanging, and noting how everybody’s attention is on the targets when the instructor gives the all-clear to shoot.

Sid unfolds the canvas tube. There’s a bow inside it within seconds, then it’s slung around his shoulder again like it was never off. Never got any arrows, but they can try again later.

Sanny is pretty sure somebody over near the siege tower just watched the whole thing, but the key is to look like you’ve nothing to hide, like you were meant to be lifting whatever you’ve just knocked. Sid is always perfect at that, strolling along giving no impression he’s in a hurry to get away. That said, it always helps to clear the scene, so Sanny suggests they do a wee circuit around the castle so they’re out of sight by the time the instructor gets back from yanking arrows oot the targets.

“Robin Hood,” Sid says as they walk around beneath the towering red walls.

“What about him?”

“Was he real?”

“Probably not.”

“Whit aboot Jon Snow?”

“Dragons again.”

“F**k’s sake.”

The castle is on the edge of a plateau, looking down steep slopes to where the Clyde flows below. There are trees screening off what lies beyond the far bank, but Sanny remembers the view from the Great Hall and the big tower when his da took him up there. It had a funny name: the Donjon. Sounded like it should be under the ground but you could see for miles in every direction.

“Naebody could get the drop on you if you were in here,” Da told him.

He used to climb the outside walls when he was wee, the damage of the centuries creating a thousand handgrips and footholds. There’s scaffolding up around a lot of it now, warning signs specifically telling you not to get too close. Towards the south-west corner, there is some kind of tarpaulin affair covering a section where the Donjon meets the outer wall. He can’t tell if they’re shoring something up or excavating.

The knight who was talking about the siege engine comes around the corner with his tour party. He’s carrying a foam sword, holding it up for them to follow him.

“I think we should join the tour,” Sanny suggests.

Sid screws up his nose, not exactly coming in his pants at the prospect of a history lesson, but he doesn’t get the purpose.

“You might no’ fancy it, but I reckon everybody else will find it riveting, if you know what I mean.”

Sid checks out the group of tourists standing in front of the guy, staring wherever he points the foam sword. Now he’s on board. The guide won’t be pointing it towards anybody’s pockets or handbags.

“The castle was initially constructed by Walter of Moray,” the knight is saying as they shuffle into place among the group. “It is believed to have been designed by Enguerrand III de Boves, Lord of Coucy, and consisted primarily of a Keep, known as the Donjon, intended to be the main lodging within a greater castle complex. The projected castle was never completed, as construction was interrupted by the invasion of Edward I in 1296.”

“Yep,” says a fat bloke with an American accent. “Builders always got an excuse why they cain’t finish the jawb.”

Sanny had clocked him for a Septic even before he opened his mouth. Boy’s gone double denim, jeans and jacket, with a trucker-style cap up top. It’s totally unacceptable.

The guide responds with a wee chuckle, then signals with the foam sword that it’s time to move on.

“Now that I’ve whetted your appetites, it’s time we took a closer look at the Donjon from the inside.”

When they come back around to the main entrance, they have to wait at the gate, as there is a steady stream of people exiting. They are all heading for the grassy field between the castle and the car park, where most of the men and women in costume are mustering. The re-enactment is going to be starting soon, by the look of it: just whenever they can clear all the weans from the siege tower.

Sid gives Sanny an inquiring look.

“Reckon we’d do better among the crowd?” he asks quietly.

“Naw,” Sanny reckons. “There’s Yanks, Japanese and all sorts in this group. Overseas tourists tend to carry a lot of cash ’cause they don’t want to be hunting for a hole in the wall when they could be gawking at statues or whatever.”

“Got ye.”

The group takes a hard right once inside, heading towards the main tower. Sanny spots the guys in the 300 outfits again, hanging about just inside the walls next to the ticket office. Maybe they’ve got some kind of surprise role in the re-enactment.

“Now, the word ‘donjon’ mutated into dungeon in common usage,” the guide says. “And when we say dungeon we think of some dank and grim underground prison chamber. But Walter Moray’s Donjon was one of the most luxurious lodgings in all of Scotland. There were opulent family apartments on the top floor, a reception hall for favoured guests on the floor below and spacious store rooms on the lowest level. If you look up at the walls, you will see a series of regularly spaced holes. These were for the beams supporting the upper floors.”

All of the tourists look up. Neither Sid nor Sanny miss the opportunity.

With his eyes focused on what he’s doing, Sanny suddenly hears the guide react in an angry voice.

“Hey. What do you think you’re playing at?”

Sanny and Sid plunge their hands instinctively into their pockets, keeping their heads down while composing their best innocent looks. Sanny can’t help stealing a glance at the guide though, which is when he sees that they aren’t the target of his outrage.

One of the blokes in the gold masks has closed the gate and appears to be locking it. The other two are already marching along the wooden walkway leading into the Donjon.

“Excuse me a moment,” the guide says, then starts striding out to meet them, pure raging.

That’s when they pull their robes back and break out the AK-47s.

Extract from Bloody Scotland - the book (HES, £12.99). Chris

Brookmyre's latest novel Places in the Darkness is published by Orbit (£18.99)