There is a deceptive simplicity about many of Agatha Christie's stories that can be both a delight and a challenge. In Verdict, unlike most of her novels and plays, the story is even simpler.

There is murder but no mystery. The audience knows who did it: the challenge is for the cast to portray why, and for the audience to try to understand their inner souls.

The play centres on Professor Karl Hendryk (Robert Duncan, still fondly remembered as Gus on Drop the Dead Donkey) and his invalid wife Anya (Cassie Raine), refugees in London who fled after helping the family of a political dissident.

Hendryk is a talented thinker with many admirers: Anya's cousin Lisa Koletzky (Susan Penhaligon) and glamorous young student and debutante Helen Rollander (Holly Goss) among them. Anya's illness debilitates all their relationships, and their tangled affections for Hendryk lead to tragedy.

The performances here are crisp and studied, but that is perhaps their downfall. The passion is not so much repressed as removed and with such a simple story the creative core of the cast is very much on show.

The faltering accents of the �migr�s detract unnecessarily from the action; as Hendryk says of student Helen - sometimes trying hard is not enough. They should drop them completely.

Elizabeth Power brings light relief as hired help Mrs Roper, but her material is thin, and director Joe Harmson's over-indulgence in these comic notes stops the play evoking the deep psychological tensions that should lie beneath the taut surface

This is good honest theatre but it needs another of Christie's twists to become great.

n Verdict is at Norwich Theatre Royal from August 1-6, �22-�5.50, 01603 630000, www.theatreroyalnorwich.co.uk