The first episode of Ordinary Lies (BBC1) was gently ridiculed in the press for having a storyline which was just a tad unbelievable.

There's nothing wrong with having outlandish stories dramatised on TV, as long as they're introduced by Roald Dahl or Rod Serling. Without those chaps, and in a drama being played straight, there needs to be at least a shred of believability in the story to stop it flapping off in the wind of silliness.

Episode three of Ordinary Lies fared no better than its predecessor. Both were enjoyable stories and well-acted, but presumably sent niggles of frustration into the viewers. Who, when watching Kathy snip and sellotape herself a fake police ID card, didn't shout, in full Paxman-mode, 'Oh, come on!' at the screen?

Ordinary Lies is a drama set in a car showroom in the glum and rainy North of England, and it aims to portray the lives of ordinary people. That's a worthy project, but the drama patronises 'ordinary people' by saying their lives are only worth watching if they have crazy, odd things happening to them. But then, the alternative to ordinary people having mad things happening is a soap, where we get ordinary people with the usual 'issues', like who's sleeping with whom and who's been punched in the bar. So how can we make 'ordinary' lives interesting? Is it only novelists who can do this, or perhaps Morrissey? How can a TV scriptwriter 'give the mundane its beautiful due'?

The answer, in Ordinary Lies, is to send the ordinary people off on a blazing trajectory of deceit, intrigue and mendacity, and this week's episode is no exception.

Kathy, the efficient, cardigan-wearing PA, takes the spotlight this week. It's already been established that she's a sensible woman, and goes home each night to her nice husband and children. It's to be noted that Episodes 1 and 3 have presented characters who possess mortgages, children and spouses - the prizes we're all meant to clutch at - yet these prim, middle-class lives are sources of tension which act as catalysts for eventual chaos.

Sensible Kathy swaps her frumpy cardigan for lipstick, earrings and a bouncy blow-dry and goes to a hotel to meet a stranger for sex. To the writer's credit, it's for nothing so 'ordinary' as an affair. Instead, Kathy's husband has been made impotent by an unspecified illness and, after years of agonising, she has decided to seek a simple and practical solution, one which she swears will not involve emotion or affection and certainly won't involve her family.

She has a splendid time and some headboards are vigorously rattled. This could have developed into a study of guilt versus pleasure, or morality versus practicality but, instead, we must be led off into silliness. Kathy and her secret lover are tumbled out of bed one afternoon by screams and hammering. They peer through the window into the neighbouring garden and see someone being savagely beaten and left for dead.

Kathy, despite being lustily dishevelled and wrapped in a sweaty sheet, immediately switches back into sensible mode, insisting they have to report this to the police. They're crucial witnesses! But her partner gets cold feet: if they do that then they'll have to explain who they are and why they were there. Their secret will be out, and two marriages will be ruined.

And so a series of lies is triggered, culminating in Kathy making herself a fake police ID card and sneaking up to houses at the dead of night, slipping brown envelopes stuffed with cash through the letterbox. Really, the story is ruined by becoming implausible. These are not 'ordinary lies'. Neither are they 'extraordinary lies'. They're just daft.