The foyer at the St Martin's Theatre, which resounds with American and Japanese tones, feels like a museum dedicated to the world's longest-running play. A large wooden board indicates that Monday night's is Performance No 18,784. Souvenir keyrings and mugs are for sale. A certificate from the Guinness Book of Records hangs near newspaper cartoons about The Mousetrap and a montage of congratulatory notes to mark the show's 25th anniversary in 1977 from such celebs as Penelope Keith, Angela Rippon and the then Prime Minister, James Callaghan.
The air of a museum-piece is carried into the auditorium. The programme states the play is set in "Agatha Christie time". Mrs Boyle (Janet Hargreaves), one of the guests at the snow-bound Monkswell Manor Guest House where the action takes place, inquires of its owners: "Do you have much servant difficulty here?" Later she fumes: "The working classes seem to have no idea of their responsibilities."
The first half is loaded with "significant" phrases. "Ah, when the snows melt, lots of things may have happened," says another guest, Miss Casewell (Angie Smith), with slightly more emphasis than is necessary. Some of the acting, too, is riper than a bowl of last week's pears. When the enigmatic Mr Paravicini (John Fleming) arrives, he practically bursts with sinister cackling (he is not alone in this behaviour; cackling must have been contagious in rural Berkshire at that time). "Yes, the unexpected guest," he laughs maniacally. "Who am I? You do not know. Where do I come from? You do not know. Me, I am the man of mystery." He proceeds melodramatically to drop a poker in the fireplace when the word "police" is mentioned.
To the show's credit, the whodunit element keeps you guessing and couples huddle over G&Ts in the interval discussing suspects. A genuine "ooo" passes across the audience when the murderer is unmasked. As the curtain falls, we are sworn to secrecy about the criminal's identity.
For all that, The Mousetrap is akin to Morris dancing: an eccentrically English ritual, loved by tourists, but not something you'd care to see more than once.
`The Mousetrap' continues at St Martin's Theatre, London WC2 (booking: 0171-836 1443)