Kat and the Kings, Tricycle Theatre, London

Critics are supposed to withhold their opinion until the review appears, but I think my neighbours at Kat and the Kings may have had some suspicion of mine when I leapt up at the end to clap as hard as I could. Considering that, for the previous two hours, the cast of six had been jumping and jiving and jitterbugging for all they were worth, it seemed little enough.

Kat and the Kings, which had a triumphant run at this address several years ago, is notable not only for its energy but for the impish charm of the five actors who make up the vocal group of the title. The story they enact is the super-flimsy one of "Let's put on a show." It's 1957, and Kat (Emraan Adams), Bingo (Loukmaan Adams) and Ballie (Munthir Dullisear) form a group with the public school boy Magoo (Elton Landrew) and his sister, Lucy (Abigail Petersen); they even cut a record.

At this point in the familiar tale, trouble always strikes in the form of one of the singer's personal problems, such as an unhappy love affair. This happens to the Kings, but not in the usual way. For the story is set in South Africa, the boys and Lucy are black and coloured, and the lover one of them takes is white. Bingo may boast, "When the chicks taste chocolate, they always want more," but the apartheid laws are no joke, and we already know that the story will end badly. For the sixth character, who spends most of the show on the sidelines, is the Kat of today (Danny Butler), who is shining shoes for a living. The presence of Old Kat flickers like a shadow behind the young people laughing and dancing and thinking they will be young forever.

Such a description, however, gives an overly somber impression. Indeed, the show at times feels too lightweight for its terrible subject, since the injustices the group suffers are only reported, not shown, and don't make much of an impression compared with the entertainment. I doubt, though, whether anything short of nuclear fission would stand a chance of impressing us when the Kings go into their high-stepping, finger-waggling, duck-walking routines. There are twice as many numbers as in most musicals, and the pastiche songs, by Taliep Petersen and director David Kramer, though sprightly and clever, are often repetitious in style and content. But one no more tires of them than the indefatigable five seem to tire of belting out their homages to Elvis, Frankie Lyman, Danny and the Juniors, and Chuck Berry. It seems a sin to single out any of them, though Adams deserves mention for his comic-lubricious swagger and Petersen for her soulful solo on "I Know the Sun Shines Somewhere in the World" and her ululations as a fine-feathered Zulu princess. But when the Kings are really cooking, they fuse into pure energy - and pure delight.

(020-7328 1000) to 8 February