Equus

That may be no bad thing ' although the Harry Potter star received positive reviews for his portrayal of disturbed teenager Alan Strang, his celebrity status must have proved at least a little distracting. Alfie Allen may have a famous sister, but other than that he's a relative unknown, and this works in his favour.

From the moment in his first scene when he begins yelling jingles from TV commercials, there's a real sense of unpredictability about Allen's performance; crucially, it's always possible to detect a vulnerable young man underneath the fixed gaze and monotone responses.

Simon Callow is Martin Dysart, the psychiatrist experiencing a 'professional menopause' while attempting to uncover the truth about the brutal act of violence with which Strang has been charged. It's a demanding role and while Callow never fails to hold the audience's attention, he doesn't convince as a man experiencing a crisis of faith. When he describes his envy of the boy's passionate obsession with horses, it feels like an intellectual position rather than a genuine emotional response.

The plot itself is the stuff of melodrama ' soap opera, even ' and as the boy's religious mother and atheist father, Helen Anderson and Colin Hurley struggle to strike the right tone. The six performers playing horses fare much better. It's difficult to explain how two-legged actors wearing metal heads can be convincingly equine, but under David Hersey's clever lighting design they absolutely are.