The danger in any one joke show is that the joke will wear thin before the show ends. The first act of Melancholy Baby!, the musical now playing at the Ars Nova Theatre by special arrangement with Second City, demonstrates exactly that danger.

During that first act, Melancholy Baby! has tried to pass itself off as a musical comedy version of Hamlet. If you don't know the story, Melancholy Baby! will do little to enlighten you. It assumes at least a basic familiarity with the story (and additional knowledge of popular criticism or analysis about Hamlet certainly won't hurt).

But the jokes grow old very quickly. Claudius and Polonius dressing in outlandishly anachronistic costumes to avoid Hamlet's accusing gaze, or the ghost from another story joining Hamlet and his father's spirit for a full musical number are funny for a few seconds, but do little to sustain laughter. When the first act ends, it's impossible to not wonder what wearying comic retreads still await.

Only moments into the second act, however, it becomes very clear that there will be a lot fewer than you originally anticipated.

Though the curtain rises on Hamlet about to begin his famous (and apparently harrowing), "To be or not to be" speech, the stage explodes only moments later into a musical revue of the songs of Heinsplatt and DeSelza, Melancholy Baby!'s composers.

Never heard of them? You'll be given a full history lesson about the intrepid songwriting duo at the start of the evening in a documentary short film about them that plays before the action proper begins. In fact, that film - terse and measured - is extraordinarily funny, probably the funniest part of the evening.

But the revue comes in a close second, with the actors from the play-within-the-play taking part in the revue-within-the-play to present some of the great songwriters' other works, including the loving tribute to a singularly beautiful city in "Akron," and selections from some of their other musicals, including The Scarlet Letter. These songs provide some of the best and most original laughs in the show; the songs in Melancholy Baby! aren't bad, but they're no funnier connected to a dramatic narrative than these are detached from one.

Eventually, this miniature diversion must end, and the "story" returns, albeit briefly, for its conclusion. But it's difficult for the show to regain its momentum, and the rest of the show ("Ophelias on Parade", essentially) certainly isn't up to the comic heights of the act openers.

Still, for all its other problems, Melancholy Baby! does have quite a bit going for it: It is excessively creative, it has a charming and energetic cast (led by Jeff Richmond as Hamlet, Michael Thomas as Claudius, and an uproarious Alexandra Billings as Hamlet's sexpot of a mother), a catchy score - actually by Richmond and Thomas - and frenetic, inventive direction (also by Richmond).

With all it has going for it, it's a shame the comedy isn't more focused, and it would make it all the funnier. As it stands, Heinsplatt and DeSelza - after the film, revue, and the hilarious program - are far more entertaining than Melancholy Baby!

Melancholy Baby!
Ars Nova Theatre, 511 West 54th Street between 10th and 11th Avenues
Schedule and Tickets: (212) 977-1700