Suranne Jones (Nancy) in Frozen
Suranne Jones (Nancy) in Frozen
© (C) Johan Persson

Bryony Lavery's play was written in 1998, long before Disney dreamt of Elsa and sent her up a mountain to sing "Let It Go". Yet oddly, her drama uses the same metaphor about the icy landscape of the heart to examine the case of a serial killer, the mother of one of his victims and the psychiatrist who tries to explain his inexplicable actions.

You can see exactly why Suranne Jones, fresh from her huge success on TV as the frenetic Doctor Foster, would jump at the chance to play the grieving mother Nancy. It's a part that runs the gamut of emotions from raw sadness, to campaigning zeal, to fury, to final forgiveness and a kind of acceptance in the 20 years after her 10-year-old daughter Rhona is snatched from the street and murdered by the predatory paedophile Ralph (Jason Watkins).

But Lavery's concerns are greater than the simple examination of grief. She introduces the unlikely character of the Icelandic-American psychiatrist Agnetha (Nina Sosanya) to (literally) give us a lecture entitled Serial Killing: A Forgivable Act? and to ask the key question: are such horrific crimes acts of evil or acts of illness?

It's an interesting exploration and the nature of the story – proceeding through a series of monologues and duologues – means it is always gripping. But the play takes a long time to get going. It is only really at the close of the first act, when Nancy is challenged by her unseen and neglected living daughter, to try to forgive that it feels as if it has reached the point it was travelling to all along. As if sensing this, director Jonathan Munby and designer Paul Wills have surrounded the actors with a lot of busy scene changes, with furniture sliding on from the sides and screens coming down from above covered in images of cracking ice and lost children. There's a lot of ominous music too from Rupert Cross.

It's abstract and arty, but I found it all a bit distracting and it increased my sense of alienation; the play is so schematic in its probing of loss and the frozen psychology of both Nancy and the abused and abusive Ralph that it is sometimes hard to get involved. The best moments are in the second half, when the pair simply confront each other over a table, sitting in silence, one trapped in pain, the other in a refusal to feel remorse. The confrontation changes things: in a chillingly effective scene Munby ratchets up the emotion by introducing a ghost like girl to underline the unravelling.

Jones is at her best in those quiet scenes too – and in the moment where she realises, finally, that against her desperate hoping, her child is dead. She's a likeable presence on stage, but I felt the performance worked from the outside in rather than the other way around. The same is true of Watkins, normally so reliable, but here, for all his anxious ticks, failing to worm his way into the soul of this tortured and terrible man. Sosanya does what she can with an almost unplayable part. The psychiatrist, trapped in her own spiral of mourning, is the least believable figure on the stage, though what she has to say about the way abuse engenders abuse is haunting.

Frozen runs at the Theatre Royal Haymarket until 5 May.