'I've taken the conventions of the thriller to see how I could bend it - how it works with a flat tyre if you like' is how the writer-director elects to describe this picture. A thriller with no thrills. A plot that makes no sense.

Isabelle (Isabelle Huppert), a virginal lapsed nun and self-proclaimed nymphomaniac sits in a cafe trying to write pornography, when in stumbles a young amnesiac (Martin Donovan). He has woken up on the street outside with a pocketful of Dutch coins and no idea who he is. Together the pair set out to recover his missing identity. Gradually, through his wife, ex-porn superstar Sofia (Elina Lowensohn) and a mysterious accountant (Damien Young) who seems to know exactly what is happening, it emerges that he is Thomas, a sadistic criminal, pursued by the violent henchmen of Amsterdam big-wig Jacques.

While there is a surfeit of plot - vague mumbling about government corruption, a computer disc McGuffin - the actual thriller elements of Amateur are pretence; Hartley is drawing in a wider audience with his fourth picture by using familiar trappings, but behind the new wrapping lurks the same idiosyncratic heart that beats inside all his pictures. His own script, while noticeably funnier, is as non-naturalistic as ever, dotted with irony and pithy non-sequiturs. A park bench discussion between Donovan and a school kid about Homer is as irrelevant as it is essential. As Thomas is always one-step behind because he doesn't know who - or more importantly what - he is, so Hartley's audience is one-step behind a film-maker whose films have always been as much about how something happens as why.

As befits his most expensive work to date (and his first city film after the more rural trilogy - The Unbelievable Truth, Simple Men and the wonderful Trust) this is a tougher, often tighter film than before - there's even a chase in Grand Central Station; a truly strange electro-torture scene; and shoot-out, albeit one peculiar enough to have strayed from one his Godardian shorts.

All melancholic eroticism, the unsmilingly French Huppert (in a part specially written for her after sending Hartley a fan letter) is excellent. As the man whose suspended identity appears to be gradually bleeding through the amnesiac exterior, Donovan has never been better. Hartley regulars Lowensohn and Young are terrific.

The slightly uncharacteristic street-level view of New York offered by Michael Spiller's limpid cinematography holds the attention, and the score, by Jeff Taylor and (Hartley alter-ego) Ned Rifle is exceptional - replacing the routine guitars for plaintive piano and violin. The knowing use of various indie luminaries on the soundtrack - The Jesus Lizard, Bettie Serveert, PJ Harvey, Red House Painters, and Hartley favourites Yo La Tengo - serves as an object lesson to Hollywood.

Only a tendency to drag things out a bit (a Hartley problem, witness the last half of Simple Men) works against the picture. But it's a small price to pay for films as warm and idiosyncratic as this.