It must be every parent's nightmare. A child goes out - and never comes back. We've all seen it on television and in the newspapers. The tearful appeals for information, any information. The police door-to-door enquiries lapping out over a widening area. Volunteers combing fields and woodland. Divers dredging canals and ponds. Still nothing.

Then, perhaps within a month, sometimes not even within a decade, the knock on the door. Something which was once a lively little girl has been found. The media excitement builds once more. There's a trial, a conviction. Then what? Bryony Lavery's three-hander, Frozen, in a new production by Michael Cabot, explores these spattered moments in time.

We meet mum Nancy on the afternoon on which she sent Rhona over to her gran's with a pair of secateurs, as much to keep the peace between Rhona and her older sister Ingrid as to prune roses. We meet paedophile Ralph as he meticulously organises himself for another "adventure". And we meet American professor Agnetha as she prepares to deliver her thesis "Serial Killing - A Forgivable Act?"

You don't have to have children of your own to find this exploration of what makes some people tick harrowing. Of course, it’s natural that sympathy goes to Nancy, bumbling along with her predictable life of slightly-straying husband Bob and two kids at the awkward stage. You don't have to sanction child pornography to understand that Ralph's terrible compulsion is rooted in his own sad childhood.

The weak thread in this skein is Agnetha. For me, she lacks the three-dimensional persona of the other characters, including those of whom we hear but who never come on stage. This could be partly due to Carolyn Tomkinson's low-key, at times inaudible, portrayal but it’s also inherent in the way Agnetha is drawn.

No such reservations about Maggie O'Brien's superb Nancy. She finds how to build inner strength from a personal tragedy, which includes the break-up of her marriage, through becoming a spokesman for Flame, an organisation that helps parents whose children have also "gone missing", right to her cataclysmic prison meeting with Ralph.

Ralph is not an easy part, but Peter Cadden shows us the whole flawed being and does so with immense power and economy of style. Hateful, yes, but in the end understandable. The irony being that it’s Agnetha who’s right about the Nancy-Ralph meeting and not the rest of us.

Geraldine Bunzl has designed an effective set for this sort of smaller-stage touring. It's a wall pasted with fading posters of missing children, rooted with red poppies and memorial candles. Cabot's direction could be tauter; there are pauses, almost longueurs, which seem to dissipate the tension. This is not a play which should give us time to think until it's over.

- Anne Morley-Priestman (reviewed at Radlett Centre)