A rare thing this - a play that actually gets better as it goes on.

Unusual and innovative, Mind Game' by Anthony Horrowitz (you may know him as the man who wrote Stormbreaker' and the rest of the Alex Rider books, or alternatively as a creative brain behind TV's Foyle's War' and Midsomer Murders') tells the story of a writer, Mark Styler, attempting some research for his latest true crime chiller.

This takes place at Fairfields, an experimental hospital for the criminally insane.

To do so, he must get past the eccentric Dr Farquhar, who has the power to grant access to his desired subject, the notorious serial killer Easterman.

All, it soon becomes apparent, is not right at Fairfields.

In some respects, this is a conventional thriller, with twists aplenty and moments of shock but there is also an enjoyable streak of absurdity.

This production matches the tricky plot with some tricks of its own - keep your eyes on the ever-changing set and props - especially the doors and pictures.

Paul Glover is assured as Styler and always believable, even when the plot twists stretch credulity. He is a calm and committed stage presence, as ever.

Julian Freeman as Dr Farquhar grows into the part as the evening continues and in the second act especially his performance is genuinely captivating.

Anna Rogers follows up her impressive role in last year's Proof' with a versatile turn as Nurse Plimpton.

The trio is smoothly marshalled by Mervyn Button, who directs at a breakneck pace, without losing the necessary subtleties.

Mind Game' does what all good genre pieces should - use the form to investigate bigger issues.

And if the themes of the nature of madness and the concept of evil are not exactly original, the ways in which they are dealt with have a spark of invention and fun.

A common criticism of stage thrillers is a lack of thrills but there are genuine moments of surprise here and the laughs (of which there are plenty) are, unusually for the genre, intentional.

This is a hugely entertaining evening, offering a welcome and refreshing change from the norm.