So a guy opens a door behind a filing cabinet, crawls up this tunnel, and finds himself inside the head of John Malkovich. That's right - John Horatio Malkovich the actor. Now, admit it - don't you wish you'd been a fly on the wall when they pitched that project?

The debut feature by skateboarder turned video director Spike Jonze has become something of an overnight legend as the most bizarre American commercial movie since Blue Velvet. John Cusack, festooned with greasy locks, plays self-pitying puppeteer Craig, who somehow finds his way into the head of America's most fastidiously peculiar actor. What's so extraordinary about the script, by newcomer Charlie Kaufman, is that it starts with an absurd wouldn't-it-be-great-if premise, dares to follow it through to its stranger ramifications and then keeps going when sanity would advise restraint.

The extremity is tempered with a very sombre treatment by cinematographer Lance Acord, and Jonze's directing style is markedly different from anything you would expect from a Beastie Boys collaborator. He favours melancholic downplaying, but isn't averse to stylistic digressions, such as a chimp's-eye flashback and the film's most unnerving sequence, where the whole world turns Malkovich.

The casting is imaginative, too - universal sweetheart Cameron Diaz is made to look totally nondescript, while Catherine Keener, usually cast as a goofy soubrette, is a crisply nasty femme fatale. Malkovich, whose part is considerably more than a cameo, relishes every moment of his demolition, as a prissy poseur who literally gets shunted up his own portal. The film is brimming with ideas, and all the certainties that Hollywood relies on - genre, gender, identity, time - are twisted out of recognition. Jonze and Kaufman have come up with what can only be called a screwball comedy from a parallel dimension. Your jaw may well drop with disbelief.