A squeaky door, a scream . . . it's 'The Mousetrap'

That creaky sound you hear is not just a door ominously opening; it's also the plot of the legendary Agatha Christie mystery The Mousetrap at the Walnut Street Theatre. The play has been running for an astonishing 60 years - it's the world's longest-running play, and for the first time its producers are permitting productions outside London.

Somehow, despite more than 24,500 performances, I managed to miss it until Wednesday night. And somehow nobody revealed the mystery's surprise solution, so look for no spoilers here.

It's a classic opening: In the dark we hear footsteps, a squeaky door, a scream, and a police siren. And it's a classic setup: a country manor, recently converted into a guesthouse run by a young couple (Jennie Eisenhower and Dan Hodge). A snowstorm. Roads impassible. Telephone dead. Five guests, all strangers.

The usual suspects are a grumpy old woman (Judith Knight Young), an annoying foreigner (Laurent Giroux), a flibbertigibbet young man (Eric Bryant), a taciturn army officer (Paul L. Nolan), and a young woman who wears men's clothing (Charlotte Northeast). There has been a murder ("Homicidal maniac!" the headlines read) of a woman in London, somehow connected to these people.

A policeman (Harry Smith) arrives (on skis!), and the rest of the play is taken up with his questioning, which throws suspicion on each person in turn. Agatha Christie, past mistress of the clue, manages to have each character drop a hint that makes our ears perk up.

And so the play creaks along, doing its old-fashioned thing, in a fine set (designed by Glen Sears) worthy of Masterpiece Theatre; the place comes equipped with a variety of backstairs and surprising doors. Director Malcolm Black allows the cast to flirt with parody without ever crossing that line, so it remains a genuine if mild mystery with a genuine if mild surprise.