Ever since his astonishing UK debut, Disco Pigs, playwright Enda Walsh has explored a series of grotesque and manic landscapes, where his characters' only way to survive is to create their own increasingly bizarre worlds, which, inevitably, collapse.

Walsh fleshes out this idea even more in this madcap tragedy, in which, holed up in a ramshackle Elephant and Castle flat, Irish emigrant Dinny and his two sons, Sean and Blake, prepare for their daily performance of a dramatised fantasy of their own lives back in Cork. The already crazed yarn becomes even more messed-up when check-out girl Hayley turns up with the bag of shopping Sean left behind.

The play-within-a-play format may look like dragged-up slapstick, but is actually a far more serious device, in which Dinny builds his brood a fortress to preserve their Irish identity, uncorrupted by the London streets. The self-deluding sentimental myth of a home that never really was may initially keep him sane, though the damage it has done to his sons is a heartbreaking display of social dysfunction and eventual breakdown.

Director Mikel Murfi never lets the action run away from itself, which makes the way the three main characters (Denis Conway as Dinny, and Tadhg Murphy and Garrett Lombard as his two boys) resemble creations from The League of Gentlemen even eerier.

At the end, the choice Sean must make, of whether to face the world alone or stay in and make up a story all his own, makes you want to shake him into life. Walsh's most ambitious work to date is a manic little masterpiece of the hidden subcultures that exist behind closed doors very close to home.