The Sinner, BBC Four

There were a great many questions running through the minds of everyone gripped by The Sinner, the American crime drama which reached its season one finale last night. But two were uppermost, for me at least: first, what was supermodel Christy Turlington doing married to some blue-collar Joe Shmoe in upstate New York? Second, why did a young mum at the beach with her husband and son decide to plunge a paring knife into the neck of a complete stranger just because she didn’t like the music playing on his phone?

The first question was easily resolved. It wasn’t supermodel Christy Turlington at all, it was actress Jessica Biel, doing her best to scrub down for the part. As for why her character, Cora Tannetti, sliced and diced the stranger, well that took some unravelling, most of it done by Harry Ambrose (Bill Pullman), a troubled (is there any other kind?) and dogmatic cop. So, this was a whydunnit rather than the more common sort, the whodunnit.

After weeks of feints, flashbacks and hypnosis sessions the why finally became evident in last night’s closing episode as Cora’s fogging trauma cleared, and all those half-remembered events and conversations coalesced into something that made sense to her, to Ambrose and, importantly, to the judge who had initially tried her for murder and sent her to prison. There was catharsis of sorts and, though other crimes were exposed and their perpetrator brought to justice (and we finally learned who was under that scary animal ski mask) we also learned that it had all been at the cost of an innocent life: that of Frankie Belmont (Eric Todd), the man Cora stabbed to death way back in episode one.

To be fair to Biel, she scrubbed down well enough to be believable as the damaged, vulnerable Cora and the nods she has received for her performance to date – nominations for both an Emmy and a Golden Globe – are well deserved. But the more intriguing character was Ambrose himself, like Cora a survivor of abuse (though his was only hinted at and then only briefly). He was socially awkward and had a difficult relationship with his wife, so he took refuge from his problems by studying the natural world – he was an expert on plants – or by falling into the muscular arms of waitress Sharon, whom he paid to punish, humiliate, strangle and beat him. It’s no surprise that it’s Ambrose who returns for season two of The Sinner, which departs from its source material – German crime writer Petra Hammesfahr’s 1999 novel – to bring us a completely new story in what now appears to be an ongoing anthology series. Currently streaming on Netflix, here’s hoping it makes its way to terrestrial TV soon.