This is a great little piece of theatre. Adapted from GK Chesterton's novel, it tells the story of poet Gabriel Syme, who finds revolution revolting and, after becoming an undercover detective, infiltrates a Europe-wide secret organisation dedicated to the overthrow of society. The seven-strong ruling council take their names from the days of the week; Syme is elected to the group as Thursday.

Attempting to foil their dastardly plans, Syme sets out on a journey during which it becomes apparent that, like him, his fellow anarchists are not always what they appear. But the question that looms largest is the identity of the elusive, terrifying Sunday.

This surreal scenario is, in Ben Harrison's clever production, cunningly played both as tragedy and farce, with the actors called to switch between the two with stunning dexterity. One minute they are donning silly beards and disguises, the next their masks are revealed as something more sinister.

As the story spirals to its conclusion the boundaries between dreams and reality become blurred. Sometimes this energetic production, with its cutout trains, hot air balloons and escaping elephants, is a tad wearing, but the inventiveness of the evening is beyond doubt.

And there is always something more serious going on behind the romp. The way in which the protagonists project their fears so vividly that they become a reality is as pertinent today as it was then. The suggestion is that it is not the anarchists who are the real threat, but our own paranoia.

Neil Irish's atmospheric design, with its host of shadowy, sinister cutout figures, sets the tone for 90 frenzied minutes during which the audience, like Syme, has every expectation shaken up. This is small-scale theatre to be sure, but it has big ambitions.

• At Aberystwyth Arts Centre tonight (01970 622882), Miskin Theatre, Darlington (01322 629472) March 14 and touring until March 24. Details: 020-7378 9787.