Coma review – so brilliantly tense you’ll have to breathe into a paper bag

Oh, the tyranny of small decisions. Sometimes by the malevolent universe, deciding to pack all the crap it can into one short day. Sometimes by the individual, often in response to the dreadful day he or she’s had. Either way, the result can be spectacularly bad.

Not quite as bad, one hopes, as it quickly becomes for the central character in the new drama series Coma. Simon (Jason Watkins) is a mild-mannered everyman, making his quiet, unassuming way through life. On his way home from the supermarket one day he shakily confronts a group of thugs who are bullying a homeless man. They laugh and chase him off. He gets home to his wife and daughter to find his car has been scratched, his neighbour Harry (David Bradley) is as unfriendly as ever, and there is letter about his mortgage arrears waiting for him. Later, he chases off a group of lads looking as if they are about to steal a car outside his house. One of them, Jordan (Joe Barber), recognises him from the supermarket. Now Jordan knows where he lives. And he promises to come back every night. Simon calls the local police but just gets a recorded message. The only practical measure he can take is to install a doorbell camera. But when Jordan comes calling the next night – and obliquely threatens Simon’s daughter – the camera records what is possibly Simon’s first ever unguarded moment. In fear, panic and rage he loses control and punches Jordan, who falls to the ground and stops breathing, as a pool of blood slowly gathers around his head. Simon administers CPR and the police, on their way to another incident stop to help and call an ambulance. It is assumed that Simon is a good Samaritan, and he tells them that he saw an indistinguishable figure run off as he arrived.

What unfolds is a similarly well-marked, wholly convincing accretion of detail that soon becomes excruciatingly tense in its authenticity. Jordan’s criminal father Paul (Jonas Armstrong) comes round to the house a few days later – ostensibly to thank him for saving Jordan’s life, as the CPR means he is now “only” in a coma and may survive – but in reality to pump him for further information about what happened that night. It is the aura of menace (you can almost see it coming off Armstrong in waves), rather than any missteps Simon may or may not be about to make, that is so terrifying. The scenes between them are those of a natural predator scenting its prey – and are almost unbearable to watch. Watkins excels in “ordinary” roles – no fake jitters here, just a deep and honest terror of the man he’s with and the situation that is rapidly getting further and further out of hand. There are a few moments – especially when he is with his impregnably arrogant young boss (who was once Simon’s trainee – one of many touches that evoke Simon’s lifetime of small humiliations) – when you wonder if Coma is going to veer into Falling Down territory. And, God, how you do long for poor Simon to rise, Michael Douglas-like, and take his vengeance against everyone, on behalf of us all. But Coma gives us these moments only to frustrate us and underline the fact that Simon’s life has always been a series of dying falls.

Coma keeps the humanity central to the story, never letting it be overwhelmed by the machinations of plot, as Simon’s defensive lies and accidental slip-ups accrue. With evidence against him mounting, the police and Paul’s suspicions gradually increase, as Harry muddies the waters. When Simon’s wife Beth (Clare Skinner – an actor who, like Watkins, specialises in making the ordinary mesmerising) becomes involved, the pressures build and the noose begins to tighten and options begin to close down.

That said, it’s not just Simon who excites our sympathy. As Paul and Jordan’s backstory is sketched in, this is not quite the black and white, hero-v-villains story it first seems to be. The investigating officer, too – DS Kelly Evans, played by Kayla Meikle – is notable for her weary kindness as she hunts for the truth, instead of the brittle cynicism or maverick tendencies we have come to expect from such a figure in such a tale.

If you can watch even the first episode of this all in one sitting, you have my great respect. I had to keep breaking off to breathe into a paper bag. By the second I was hiding behind the sofa. But at least I know now never to buy a Ring doorbell, or enrage my grumpy neighbour by demanding an occasional “Hello” from him in the middle of a police investigation. The mild-mannered need to stay in their box. We are not designed for lashing out. No good ever comes of it.

• Coma is on Channel 5.