Rarely have I been so wrapped up in a drama right to the last minute. The tension built to perfection; the little clues dropped; the alibis pared away; the relationships shredded; and the motives piling up all over the place. Almost without exception, the characters were perfectly realised, with the edgy relationship between "The Children" being perhaps the most realistic of all. And then what happened? Possibly one of the biggest cop-outs ever to darken the screens of British television. What a huge, gnawing, disappointment.

See, I'm old school me. I like my loose ends tied up. I like to KNOW whodunnit. My side of the bargain is to give you, ITV - you, Lucy Gannon - three hours of my life in which I sit and let you entertain me. Your side is to package up a dramatic, challenging, believable, complex story with a great pay-off. And you know the really frustrating thing? For 170 of those 180 minutes, you did just that.

All the wrangling about whether to report Jack to the police, and rip this shredded post-modern family "unit" even further apart with Child Protectiion and Social Services and suspicions flying about landing where they will, caught Jack, Cameron, any other potentially shifty-looking bloke who happened past in its wake.

"I didn't touch her!" wailed Jack, and Cameron's reply was chillingly accurate: "All that matters is she says you did."

So they agreed, Cam and Sue, that Jack would never set foot in the house again. Blown out by his mother, who isn't seen much and when she is appears to be planning a last-minute break to Cyprus, Jack turned to babysitter Mary for solace. She does a good line in solace, does Mary. "I know you didn't do it," she said, "you were a virgin until - what? - half-12 yesterday."

Sue, somewhat belatedly, worried that the tension, suspicion, and accusations would split her and Cameron up. He was a bit non-committal on the subject, perhaps because he's boffing Polly Hamilton in a disused classroom. I don't know. The slightest bit of trouble and he's off to the next conquest. The path of least resistance. Where does that lead, do you suppose?

Time was catching up with the retrospective plot, as the police began to unravel the complex interactions which we've seen playing out over the past couple of weeks. Emily suffered a broken neck, which stopped her breathing, and a fractured skull. And she was a virgin which, ironically, let Jack off the hook, although he never knew of his vindication. The baby, said the DCI, is the only one with an alibi.

And so we arrived at the last ten minutes of what had so far been an excellent drama, and began to play through what could have been a very clever device: the dramatisation of each policeman's suspicions of which one of the many players with a motive actually caught up with Emily that afternoon in the back garden. Was it Cameron, returning to Sue's to collect his AA file? "My Mum says you're not to come here any more," Emily lied, inflaming Cam's anger with the aforementioned results.

Or perhaps Emily's Dad Paul came home unexpectedly and was so incensed that her actions had caused a rift between him and Natasha that he couldn't control himself?

Or was it Anne - dropping off her note informing Cam and Jack of her 2-week Cyprus sun-break - who caught sight of the open garden gate and in a sudden rage, did the deed? "I could gouge out that little madam's eyes," she had said to her friend earlier. Or, maybe, break her neck?

The most likely suspect, the falsely accused Jack with no home, no family and no friends had "left my iPod at Sue's" and came around with new, angry, girlfriend Mary. Things were already out of hand when it was just Em and Jack tearing chunks out of each other, but with Mary in tow anything could have happened.

Each of these possibilities played out. Each, in their own way, plausible. I found the most believable culprit was Cameron, but maybe that's just because Kevin Whately is such a good actor. In terms of the story, the most probable perpetrator was Jack. And maybe that is the point. That each of us watching would bring our own prejudices and preconceptions to the table and pick one killer from the list, just as the investigating police would. Clever, but ultimately unsatisfying.

And that final scene? Natasha sitting alone, blubbing, saying to no-one that she was sorry? Are we meant to interpret that as guilt? The only player with no vignette showing how she might have done it? What excuse she had for going to the house, or knowing Emily would be there? What is it - post-natal depression or something? Too many questions, and not enough conclusions. Sorry, but right up until the last of those disappointing ten minutes, this could have been a really good ending. If it had been, then the multiple-motive scenes would have been, in retrospect, a touch of genius. Without a final clear resolution they turned into a kind of meaningless parlour trick.

The Children: Episode 1 | Episode 2