It starts with a small act of kindness, when a sympathetic young barman offers a free cup of tea to a teary middle-aged woman who enters his pub. But Martha very clearly isn’t who she claims to be, and their friendly banter soon spirals into a harrowing, claustrophobic nightmare when she turns into a full-on stalker.

This is the terrifying real-life experience of comedian Richard Gadd, who first told this story in a powerful stage play at the 2019 Edinburgh Fringe. Now, the seven-part TV adaptation of Baby Reindeer, named for Martha’s ‘affectionate’ nickname for her victim, expands on that, delving even deeper into the broken psyches of all involved. 

As well as writing the series, Gadd plays the fictionalised version of himself, Donny, who becomes embroiled in this mess. However, what makes this psychodrama compelling is not so much the peril he is in, but his complicity in making it happen, even after learning pretty quickly just how dangerous lonely fantasist Martha can be. 

Donny knows full well he should shut down the contact that encourages her, but he’s damaged, too. He desperately needs validation – that he is a struggling open-mic comic tells you that – and he can’t bring himself to close off the only positive affirmations he’s getting in life.

In this, Baby Reindeer’s narrative is driven almost like a comedy, with a man’s inherent weaknesses leading him to make the worst possible decisions, sending him ever deeper into trouble. But here the consequences are traumatic, not farcical, and it can be difficult to watch the self-destructive Donny sow the seeds of his own future torment.

As a writer, Gadd is unflinchingly honest about his failings, and as an actor, he relives his trauma so viscerally that it’s almost painful to watch but so mesmerising you can’t look away.

Meanwhile, Jessica Gunning deserves every award going for playing Martha, variously sad, vulnerable, furious, predatory, psychotic and playful – sometimes all in the same conversation – and make it credible. Her pained humanity brings depth to a character that’s way more complex than an obsessive bunny-boiler, just as Donny is more complex than being an entirely blameless victim.

Directed with flair by Weronika Tofilska, whose feature Love Lies Bleeding is also out soon, Baby Reindeer’s tone is as layered as its story – even with occasional flashes of the darkest humour, although no one would ever mistake this for a comedy. But is brilliant TV.

• Baby Reindeer is out now on Netflix. Richard Gadd talks about the show here.