Theatre: Some Sunny Day Hampstead Theatre, London

The best magicians leave you rubbing your eyes in disbelief. You know it's a combination of skill, illusion and flourish, but you end up swallowing it whole. The trick for a playwright is to push the illusion and the audience's sensibilities as far as possible. Some Sunny Day, Martin Sherman's surprising dramatic comedy, reveals him as a splendidly cunning conjurer.

A sunny poster depicting a camel caught in the middle of a Carmen Miranda impersonation alerts us that we're probably not up for yet another quasi- naturalistic slice of London life. Holed up in Cairo in the summer of 1942 under threat of German invasion are confident Rupert Everett as Robin, a New Zealand reporter with a mysterious background and no sense of vocation, and David Bark-Jones as Alec, solidly British as the officer with whom he is sleeping. This unlikely household also comprises Sara Kestelman as a Russian duchess, Corin Redgrave as Horatio, a minor embassy official besotted with a belly dancer, and Cheryl Campbell, devouring every comic moment as Emily, his despairing wife with one lung and a penchant for grand passion.

In his early and riotously funny play, Cracks, Sherman threw in enough red herrings to furnish a fishmongers. Here, he plays a similar game with suspicion, secrets and surprises, gunshots and even a murder, but this is no conventional thriller. His ambitions are far greater.

At one point, Robin wonders whether an artist is part of God and for one moment you think you're in for a re-run of Amadeus. In fact, beneath the enjoyable comic surface, it is about serious moral dilemmas facing the artist: the consolations of fantasy versus the power of imagination, acting versus feeling. Driven to distraction by her husband's destructive fantasising about his new love, Emily attempts a little voodoo to dispatch her "tummy-dancing" rival and becomes hysterical. At the emotional climax she suddenly breaks, announcing to her friends, "I have just given a mad scene." It's simultaneously affecting, funny and illuminating. By contrast, the seemingly feckless Robin's heartfelt imaginative visions are revealed as compassionate and altruistic.

Actors will tell you that meaty characterisation is woefully rare, but it's one of Sherman's trademarks that signal the genuinely theatrical nature of his plays. Director Roger Michell seizes upon this and paces his detailed production with his habitual care, giving his cast physical and emotional room to manoeuvre the dramatic mood-swings of the text. The characters all dream of leaving but by the unexpected end of this impressive play, it is the audience who have travelled furthest.

To 1 June. Booking: 0171-722 9301