Why was Five Days called Five Days? I guessed it was going to be like ITV1's hit Collision, each of its five episodes (1 to 5 March, 9pm) turning on a different but consecutive day during a police investigation. But no. Like the first series in 2007, the first two parts concerned the events of 48 hours or so: this time the leaving of a baby boy in a disabled loo and the apparent suicide of a man wearing a burqa (he threw himself in front of a TransPennine train and caused a terrible mess; Leeds just had to wait).

Yet part three began with the words "one week later"; part four covered "day 37", though not that much had happened since the previous night; and part five was "day 102". I can only conclude that the title was a reminder to viewers to tune in every weekday evening. A bit feeble, this. Get your audience hooked, and they won't need any reminder.

But this isn't the only reason I'm bewildered. I loved the first two episodes and boasted to anyone who would listen that I'd discovered the new State of Play. The plot was involving and every character connected to our crime - it became apparent that Burqa Boy might have been pushed - in ever more intriguing and silky ways, cobweb-style.

Also, it had a great cast. Among the cops were Suranne Jones, late of Coronation Street, as PC Laurie Franklin, and David Morrissey as her boss, DI Mal Craig. Morrissey is the greatest fun a girl can have in front of the telly on a weekday evening. He is such a dish, especially compared to most conflicted TV policemen (no one longs to be alone with a cold limoncello and, say, Ken Stott).

Franklin's mother was played by the wonderful Anne Reid, and her mother's fancy man by Bernard Hill. Kevin Doyle (The Lakes, At Home With the Braithwaites) was a twitchy forensic expert with a special interest in shoes ("That's a bunion to you, darling"). Doyle is always superbly weird, and frankly more could have been made of his character. Call me kinky, but I would have liked the DI to have caught him surreptitiously sniffing the victim's insoles.

Then it all started to go wrong. Questions, questions. Why was one lady copper left to prowl an estate full of feral children on her own? Coppers work in pairs. Why was a man asked to foster the abandoned baby by a social worker who was also the sister of his dead wife? There are rules about these things. This being West Yorkshire, there were lots of Muslim characters: nice ones, who drove taxis and didn't take it to heart when old ladies asked them where they were from, and naughty ones, who went to terrorist training camps in Afghanistan (though they regretted this afterwards - Five Days was nothing if not politically correct, and strove hard to suggest that these boys were not bad, but "lost").

Danny (Matthew McNulty), who worked on the TransPennine Express and had witnessed the burqa suicide/murder, was a convert who had married his childhood sweetheart, Nus (Shivani Ghai), one of the nice Muslims. They were trying to adopt a baby, preferably the disabled loo baby, whose picture they'd seen in the evening paper. I believed in their relationship about as much as I believe in fairies, elves and England's ability to win the World Cup.

When I wrote about Collision, a furious producer tried to ban me from seeing an ITV drama preview ever again, on the grounds that I'd given away the twist. I will try not to commit the same heinous crime here. If you have not yet seen the final episode, suffice to say that the various plot threads do somewhat fall away, leaving only a sad old prostitute and her favourite client for one to chew on.

I suppose Gwyneth Hughes, as the writer of Five Days, was trying to make some neat point about our present state of paranoia: apparently, when it comes to crime, we should worry about needy hookers, not young men with extravagant beards. But it didn't work for me. I was all dressed up, ready with my cushions, behind which I hoped to hide when the thrills really started, and then she went and left with me with no place to go but Huw Edwards, the ten o'clock news, and a feeling of having wasted five hours of precious viewing time.

Five Days is shown on BBC1.