Poprishchin (Robert Bowman) is falling apart in spectacular style – his job is getting to him and he has a superiority complex. He can't stop sharpening pencils, like a bizarre ritual. Anti-Semitic, misogynistic tirades give way to extended jags of weeping, and he swears he spoke to a dog, the dog understood every word,and spoke back. His love interest, Sophie, is proving as elusive as a dream which disappears in the morning.

Both utterly tragic and black dog- funny, this one-man monologue is ferociously portrayed, with a torrent of stream-of-consciousness language, and all punctuated by a fine brooding score by Roland Melia. As Poprishchin steadfastly refuses to go into work, claiming that he is fact the King of Spain, his delusions become evermore entwined with his daily living. Pronouncements on life become increasingly grandiose, like 'the moon was made in Hamburg'. He fashions a cloak from a newspaper, and insists on being referred to by his title when he does eventually leave his home.

If the outcome is clearly sign-posted right from the start, it doesn't really matter. Diary of a Madman is a reminder of the possibilities of what low-key staging and a compelling presence can do.

Zoo at the Pleasance, 140 Pleasance (0131 662 6892) 7– 30 Aug ( not 16, 23).