Bill Murray is Wallace Ritchie, an American video-store clerk arrived in London to pay a surprise visit to his brother James (Peter Gallagher). James, however, has a dinner party planned, and to get rid of his dullard brother he treats him to a night of something called "The Theater of Life," a brand of interactive action-adventure street theater.

Implausible, yes -- but it gets better: The hapless Wallace stumbles into the middle of some real-life subterfuge, complete with murderous thugs, sinister pols, and a sexy siren (Joanne Whalley). While the bullets fly, Wallace remains blissfully ignorant, responding to mortal danger with such aplomb that he wins the respect of the intrigue community, the heart of the vamp, and the day. Like Chauncey Gardiner in Being There, Wallace finds that his naïveté is his greatest asset.

This is, of course, a stock, one-joke plot. But Murray's boundless comic versatility keeps things going. Indeed, half the fun is the eye-flickering sensation of watching him stretch the joke without letting it snap. After all, every good thriller needs tension.