Without You, ITV1, Thursday After Life: The Strange Science of Decay, BBC4, Tuesday

Anna Friel puts in a leaden performance in a thriller in which very little rings true

Strange affair: Anna Friel plays a woman whose husband is killed in a car crash, supposedly with his secret mistress ((C) ITV )

Here's a conundrum: Greg and Ellie Manning are a thirtysomething Manchester couple.

She's a primary schoolteacher; he's an accountant. They're trying, a little desperately, for a baby. When Greg leaves for work one morning, they're both anticipating a night of strenuous, post-prandial baby-starting. That evening, Greg rings to tell Ellie he'll be late and she replies, "Be here by nine or don't bother coming home." Uh-oh. You just know she shouldn't have said that. He's not back at 9pm. At 9.45 there's a knock on the door. Ellie finds herself looking at two policemen, who inform her that her husband's dead. Car crash. Horrible burns. And incidentally, says the granite-faced lady cop, there was another woman in the car ...

The woman turned out to be Milena Livingstone, an events organiser; her website revealed that she was blonde and rather thrillingly glamorous. At the inquest, Ellie learned that the car went out of control in a dead-end road visited only by joy-riding kids "and shagging couples"; abruptly her mind was filled with lurid imaginings of Greg having his ear nibbled by Ms L. But she also learns a crucial detail: Greg, a chronic control freak, wasn't wearing a seatbelt when the car went off the road. As everyone around her assumes that her husband was having an affair, Ellie tries to prove them all wrong. "There's sumthin' not rahhhht about it," she says several times in Mancunian.

Without You is written by Charlotte Jones from a novel by Nicci French, the double-headed thriller team well known for the subtlety of their plots. Sadly, there's little subtlety here, in direction, characterisation or casting. I've watched too many thrillers where the action is advanced by a teensy piano figure (like in Don't Look Now) where consternation is expressed by a tilted camera, and misery by rain on a window. And the characters lacked credibility. Early on, we watched Ellie being warily loving in the kitchen with Greg, then kindly understanding in the classroom with a nervous kid. But Anna Friel's performance soon became a one-note, northern-harridan yell of suspicion to all. An old lady at the inquest told Ellie how lovely Greg had been with her, but something in Marc Warren's rodent face and cruel eyes makes it hard to imagine him a warm-hearted accountant. Making the enigmatic Milena a party planner seemed a pointless nod to the Middleton family. And Milena's lugubrious cuckolded husband ("I never expected exclusivity") seemed too old, too Londonish and too quickly convinced that his wife had been laying more than the tables when Greg was around. None of it rang true.

Part one ended on a cliff-hanger, as Ellie talked her way into Milena's business premises. I'll watch the outcome for Ms Friel's sake, but otherwise Without You was a bit Without Fire.

A different kind of post-mortem drama unfolded in After Life: The Strange Science of Decay, the record of an unsettling experiment. Dr George McGavin, a chortling, bearded Scottish expert on decay, rigged up a glass-walled kitchen with food and drink – a chicken, a whole pig, fish, fruit and vegetables, cheese, sandwiches, cakes, chilli con carne and bottles of wine – then left it to rot for eight weeks while he popped in with fellow experts to dilate on aspects of putrefaction.

Some of the programme was poetic ("The fate that awaits all things – to be broken down, to be recycled, to be reborn"); some rather boring (a long digression into supplying sandwiches to the US army); much of it was disgusting (I simply cannot bear to describe the unspeakable chicken), but much was fascinating. How colonies of bacteria send signals to each other like an invading army; how slime mould can find its way to food in the centre of a maze. After 30 days, 10,000 flies – mostly drunk from the alcohol in the fruit bowl – were wholly in charge. I bailed out on Day 44 when the beetles arrived and the Prof discovered 1,000 flies in a bottle of claret and insisted on presenting fistfuls under our noses. The hunger for knowledge can go only so far.