'The Book of Mormon," the jubilant and expert one-joke Broadway musical by Trey Parker and Matt Stone, is everything you should expect from a show by the heat-seeking rascals of "South Park." What you may not expect, however, is the sweetness.

Of course, there's lots of dirty talk. Unlike the frat-boy sniggering in Hollywood's stunted comedies, however, the sensibility of this live satirical cartoon has the self-delighted shock value of a naughty schoolboy.

advertisement | advertise on newsday

Naturally, there is nonstop irreverence, which will be offensive to some, most understandably to Mormons. But Parker and Stone describe their wildly original musical comedy as "an atheist's love letter to religion." And for all the ridicule bludgeoned on the faithful, the musical seems smitten with the basic desire -- however twisted and self-deluded -- to do good.

Josh Gad and Andrew Rannells are mercilessly right as the mismatched young missionaries -- one sloppy and needy, the other golden and driven to do "something incredible," preferably in Orlando. They are dispatched from the idyllic regimen of Salt Lake City to a Ugandan village where, somehow, Parker, Stone and Robert Lopez ("Avenue Q") deal with AIDS and genital mutilation without turning the musical comedy into a tragedy.

With co-director/choreographer Casey Nicholaw ("Spamalot"), Parker and Stone also have made an outcasts' love letter to musical theater. The melodies are simple and serviceable, with a shiver of what one boy calls "Donny Osmond flair." The lyrics are tough and clever. Nikki M. James, lovely as the village girl, sings about wanting to go "where the flies don't bite your eyeballs."

Scott Pask's sets are heavenly painted flats for America, theatrical squalor for Africa, with dioramas for Biblical flashbacks to upstate New York. The scrubbed young zealots in their black pants and white nerd-shirts do endearingly repressed disco dance with pumping limbs. Only the Africans -- perfect in happy-villager mode -- are allowed to move their torsos.

advertisement | advertise on newsday

The pop-art puerility gets tiresome, but the high-quality craftsmanship never does. And note, please, the Africans' fractured-assimilation production number, a hilariously terrible and learned homage to "The Little House of Uncle Thomas" from "The King and I." As Beckett -- or was it Cartman? -- liked to say, nothing is funnier than unhappiness.