The line that turns up again and again in

Ain't Misbehavin'

is, "One never knows, do one?" Good to keep in mind as you sit through Act 1, wondering why the show - chock full of great Fats Waller songs - seems so flat. They sing "The Joint Is Jumpin'" but it's not. And then, in Act 2, the show leaps into life and everybody at the Prince Music Theater starts having a much better time.

So, true enough: One never knows.

Fats Waller wrote and/or recorded the show's tunes during the Harlem Renaissance in the '20s and '30s. There are the famous numbers like the title song, "Ain't Misbehavin'," and "'T Ain't Nobody's Bizness If I Do," "I'm Gonna Sit Right Down and Write Myself a Letter," and "It's a Sin To Tell a Lie."

The show is a musical revue - with no plot and nearly no dialogue - and the set is a few cabaret tables with a bandstand onstage (and six excellent musicians, led by Eric Barnes at the piano), and garish lights suggesting an old-time nightclub.

Melba Moore, the show's headliner, known for her four-octave voice, appeared in the original production of Hair and she's still looking good. Her rendition of "Mean to Me" is very moving and, unlike her other numbers in the show, it showcases her voice and her delivery.

Act 1 seems overdone - too much miking and hyping when there's no need to sell it to us. And wouldn't it be a pleasure to hear these voices belt it out without amplification?

Act 2 has distinct moods - funny, pensive, noisy, quiet. It also gives everyone a chance to shine: Andrea Dora, who seemed hyperactive and screechy earlier, delivers a smooth, ripe rendition of "Keepin' Out of Mischief Now." Eugene Fleming and Ken Prymus are great together in the comic duet, "Fat and Greasy," following the female comic duet, with Moore and Chanta C. Layton singing, "Find Out What They Like."

Fleming pairs with Gabrielle Hurtt in "That Ain't Right" and Ken Prymus does an entertaining version of "Your Feet's Too Big." The whole company gives us a lovely and mournful "Black and Blue."

Ain't Misbehavin' has been a Broadway staple since its premiere in 1978 when Richard Maltby Jr. and Murray Horowitz created the show. The Prince's production provides some good holiday entertainment.

Ain't Misbehavin'

Conceived by Richard Maltby Jr. and Murray Horowitz. Songs by Thomas "Fats" Waller. Directed by Richard M. Parison Jr., choreography by Mercedes Ellington, costumes by Mark Mariani, sets by Todd Edward Ivins, lighting by Shelley Hicklin, sound by Nick Kourtides.

The cast: Melba Moore, Eugene Fleming, Ken Prymus, Gabrielle Hurtt, Chanta Layton, Andrea Dora.

Playing at Prince Music Theatre, 1412 Chestnut St., through Dec. 31. Tickets $25-55. Information: 215-569-9700 or www.princemusictheater.org.

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