Once Upon A Mattress, Landor Theatre, London, ***

I've always thought that "The Princess and the Pea", in which a mysterious stranger proves she's really royal when a pea beneath 20 mattresses makes her toss and turn all night, was a terrible story. I mean, consider: On a stormy night, a lass with no attendants, money, or ID turns up at the local castle and announces she's a princess. She's given a change of clothes and a bed for the night, but when she comes down to breakfast the next day, what does she say? Is she grateful? Is she even polite? No, she complains that her bed was so uncomfortable she couldn't sleep a wink. So the king and queen, rejoicing at having found a girl so sensitive, tell their only son: "Here's your bride." Poor kid – getting hitched to the medieval equivalent of Princess Margaret.

Mary Rodgers (daughter of Richard) also thought this story was pretty fishy, and in this delightful 1960 musical, provides, with lyricist Marshall Barer, a far more plausible version. Prince Dauntless, who couldn't have been worse misnamed, is clamouring to get married, but his dragon mother, Queen Aggravain, makes sure that every applicant fails the princess test by devising a new one each time. The courtiers are wretched too, for everyone is forbidden to marry until Dauntless does. As they chorus miserably, "No one's getting any... younger." (That's as racy as the jokes get.) With desperate measures necessary, a bold knight rides off and comes back with Winnifred of the Swamp Country – not the most feminine princess, but a really game girl.

By using actors who can double as musicians, the plucky little Landor Theatre has managed a production lavish by over-the-pub standards, with up to five instruments on the go at once. But, more important, the actors in Robert McWhir's cast are talented and sparky, especially Dian Perry as the leech-like queen, Nick Dutton as a conspiratorial minstrel, and Ciaran O'Keeffe as a lady-in-waiting who's hot to trot. The only performances that are off key are William Maidwell's prince, who seems afflicted rather than backward, and Ian Dring's king, who is creepy rather than goofy in his silent (he has been struck dumb by an angry fairy) pursuit of anything in a medieval skirt.

The score includes lilting romantic ballads as well as plenty of comic numbers – Winnifred, though quiet deep down, announces herself with "I'm shy!" and the courtiers join Dauntless in his happy declaration "I'm in Love with a Girl Named Fred." The delicately-built Donna Steele is odd casting for this tomboy part , but she rises magnificently to it, punching well above her weight with a robust manner that never misses a comic trick. Instead of "Spit in your hostess's eye", the moral here is the much more satisfying one: "Work your butt off, and you'll clean up."

To 7 June (020-7737 7276)