Bully Boy (Mercury Theatre, Colchester)

There's an added poignancy to a play like Bully Boy when you watch it in a garrison town on Remembrance Day. Sandi Toksvig's dark military drama, commissioned in 2011 by the Nuffield in Southampton, is a world away from the playwright's more familiar comic persona and, in her own words, it's "full of rage".

That rage is not always helpful to her as a dramatist. The two-hander is both a compassionate study of post traumatic stress disorder and a pacifist's howl of anger against the establishment, and the two occasionally tread on each other's toes. From time to time Andrew French's wheelchair-bound Oscar has to break out of his role as a Major investigating a possible atrocity committed in Afghanistan by young Gunner Eddie (Josh Collins) in order to mouth left-over arguments that Toksvig hasn't managed to shoe-horn into the action.

That's a pity, because Bully Boy is only a good editor away from being a good play. For most of its 90-minute duration it is taut and fierce, and it's veined throughout with telling dialogue. "I lost the use of my legs because I went to war" says the Major. "And I lost my mind" rejoins Eddie. As mental health finally pushes its way onto the nation's political agenda, this is timely stuff.

With the exception of an ill-judged recording of Toksvig herself reading the news, Dan Sherer's new production is flawless. Imaginatively lit by Charlie Lucas and set amid harshly evocative designs by James Cotterill that suggest both the Afghan chaos and Eddie's fragmenting mental state, the young director sustains tension by injecting a vacillating see-saw of compassion into the two men's relationship.

It helps that his actors are both exceptional. Collins tips from cheeky chappie to loose cannon in a heartbeat, his mental scars practically bleeding from his soul. "Not a mark on me" he declares, grimly. French, in a less showy role, gradually reveals the Major's own issues and a complicated past of his own from which he has now recovered. Almost.

During a scene when they share a drink the actors are saddled with an awkward episode of sardonic authorial humour. You'll be glad when it's over. The town of Burnley comes in for some stick, too, since Toksvig is never one to shy away from an easy target. But if Bully Boy is flawed, it's still a valuable play on a subject that's under-discussed and little understood even today.

Bully Boy runs at the Mercury Theatre, Colchester until 21 November.