Karma:Coma.

Simon (Jason Watkins) and Beth Henderson (Claire Skinner) are a lower middle class, middle age couple living in textbook suburbia somewhere in Cheshire (though, surprisingly, filmed in Budapest). Their life is one of supermarket wine, fish fingers, chats about bin days, and stultifying dull office jobs. Their pride and joy is their adorable, and asthmatic, pre-teen daughter Sophie (Matilda Firth) who likes jumping on beds and running around in the park. Like most kids.

One day, on the way home from the shops, Simon nervously intervenes when he witnesses a gang of youths picking on, and beating up, a homeless man. Predictably they turn on Simon. Especially Jordan (Joe Barker). Simon's car is keyed, Jordan forces his way into Simon's house, and accuses him of being a 'paedo' - standard.

Instead of walking away, mild mannered Simon lashes out. He punches Jordan and, somehow, knocks him out. Even more incredulously, Jordan goes into the coma that gives the Channel 5 show its name. Coma (directed by Michael Samuels, written by Ben Edwards) follows what happens to Simon, and Jordan, following this life changing event and it turns out to be tense, very tense, painfully tense towards the end, and eminently watchable from start to finish. Not that there's a great deal of competition but it's one of the best things I've ever seen on Channel 5.

Simon tries CPR on Jordan and soon the police arrive - on their way to deal with another incident. Simon lies to the police about what has happened and then lies to his wife Beth as well. Understandable moves but inadvisable - and necessary for the drama to have legs.

Beth, a nurse, is rational, sensible, and level-headed and she's clearly very supportive of, and in love with, Simon. A man who seems anxious enough before all of this. With good reason too, he's being pursued by his mortgage company and he's being made redundant from his job by his boss Jimmy (David Mumeni), a cookie cutter arsehole straight from central casting.

A narrative takes hold that Simon has saved Jordan's life (a local paper carries a picture of Simon with the headline 'LOCAL HERO') and soon enough Jordan's father, Paul (Jonas Armstrong), arrives to thank him - and becomes very insistent that he treats Simon to a pint. Paul, like Jordan, is trouble. Big trouble. Some kind of gangster, he's also an unlikely oenophile and speaks fluent Spanish. Paul likes Simon - but still scares him. That's nothing compared to what will happen if Paul ever finds out the truth.

DS Kelly Evans (Kayla Meikle) is assigned the case and she, too, will be taken on a long and winding journey towards the truth - or something close to it. The first episode sets up the story and the next three see that story unravel as Simon, of course, finds himself in way over his head - on multiple levels. He is dragged into Paul's world of violence and criminality (and worries that Beth and Sophie will be pulled into it too) but, by his very action of punching Jordan - something he won't be able to pass off as self-defence, he has become a violent criminal himself. If, unlike Paul, a reluctant one.

As we wait to see if Jordan will survive (and if he does just how much danger will Simon then be in) we're dragged into Simon's new world of blackmail, drugs, guns, life support machines, missed calls, threats, extortion, abandoned warehouses (but of course), and one seriously awkward vigil. Filmed with Dutch angles and dramatically and sometimes jarringly scored by Samuel Sim, Simon spends much of Coma hyperventilating, having nightmares, and furiously washing his hands like Lady Macbeth.

Watkins is a masterclass in panicking nervous energy but every one else is good too (props go to David Bradley as Simon's irascible neighbour Harry, Kwadwo Kwateng as Mason - another young criminal and gang member who has 'beef' with Jordan, and Adrienne Reti as Jordan's underused mother. I thoroughly enjoyed Coma and it was to the maker's and performer's credit that, at no point during it, was I certain how it would all resolve itself. Or even if it would resolve itself. A show that starts with a punch - in more ways than one - always seemed likely to end with one.