One Day All This Will Come to Nothing, Traverse, Edinburgh

There's a moment in the 1988 Dutch film The Vanishing in which a man hunting for his missing wife is given a horrifying choice: drink from the drugged flask offered to him by a man who may be his wife's murderer, or walk away never knowing whether she lived or died.

There's a moment in the 1988 Dutch film The Vanishing in which a man hunting for his missing wife is given a horrifying choice: drink from the drugged flask offered to him by a man who may be his wife's murderer, or walk away never knowing whether she lived or died. Driven beyond the point of madness by his grief, he slugs down the contents of the flask.

Nothing quite as gruesome happens on the surface of Catherine Grosvenor's debut play about the void left when someone disappears, but there are plenty of characters ready to drink from the hypothetical flask. Because what do you do when someone you love vanishes? What do you do when you don't know whether they've jumped ship to live another life, or jumped off a bridge? When do you stop searching?

Early one morning, Anna, a policewoman, is called to deal with a body found washed up on an urban waterfront, uncomfortably aware of the disappearance of her own boyfriend Mark five days previously. In a desolate field, a boy digs his own grave because he wants to be "under the soil" and not found. Ever. A man sits down in the road, spewing the contents of two plastic bags, but doesn't recognise the name on his library card. In Grosvenor's world - or Anna's - there are endless permutations of Lost.

There are some desperately moving moments in this play, and an occasional refreshingly surreal kick. Director Philip Howard initially creates a nice ambiguity, but there's a jarring fault line, 10 minutes in. Just when we're soaking up the sublimely tragic image of the boy digging himself a hole to die in, enjoying not being able to decide if he is dead or alive, in Heaven or in Hell, we're plonked unceremoniously into a city-centre club in which his saviour is a guardian angel with rather more earthly desires.

Despite this inconsistency, a very strong cast gives some great performances, notably Molly Innes as Anna, who injects an enormous truth and subtlety into her portrayal of a woman faced with the impossibility of grasping the unknown. In WPC Anna's black-and-white-checked world, everyone is missing, amnesiac, kept in a cage in a wardrobe or fished out of a river, unrecognisable - and this time, it's personal.

If anything, the screw is turned just a little too tight on all these lost souls, whether they're the boozers who abandon their belongings or the father come from abroad to photograph the body of his murdered daughter so that his wife will see, and therefore believe, that she is dead.

Amid flashes of taut writing, the dramatic flow is sometimes dammed, with no palpable sense of time passing. In a play about not knowing, it helps to have some anchor with which to gauge the abyss of the unknown. But when the threads are skilfully drawn together in the final moments, we are plunged into the heart of what it means to lose and to live on.