There's one reason to see Roundabout Theater's revival of the 1978 musical "On the Twentieth Century":

Kristin Chenoweth.

The play is set on a luxury passenger train speeding from Chicago to New York in the 1930s. David Rockwell's art deco sets are luscious, and William Ivey Long's costumes — especially the fur-cuffed robe Chenoweth lounges around in while in her first-class compartment — bathe us in pre-war glamour. But it's Chenoweth who takes a so-so operetta score and stuttering book and propels it into dizzying heights with her comedic gifts. 

Chenoweth plays actress Lily Garland. We first meet her as Mildred Plotka, a frumpy, mouthy, piano accompanist from The Bronx, brought in to play piano for a fading star's audition. In perhaps my new favorite scene in musical theater, Chenoweth as Mildred talks back to the star and the producer, and gets the part. 

It's hard to overstate how excellent Chenoweth is in this role. She nails all the small details, from the pitch-perfect operatic notes to the upward flip of her hands as she makes it clear she doesn't care that she's in front of a famous producer. She brings an authenticity to Mildred — and then Lily Garland, her stage name — that keeps the madcap scenes she's in from running off the rails.

Chenoweth is the star of the show, but her character is not the narrative driver of the play. That role goes to Oscar Jaffee, the down-on-his-luck producer who once gave Mildred her shot. His only chance to turn his life around is if Lily signs a contract with him before the train pulls into Grand Central Terminal.

Peter Gallagher plays Oscar as a narcissistic charmer a lot of warmth, but no vulnerability. His rival for Lily's affections is Bruce Granit, played by Andy Karl, who was Rocky on Broadway last year. It turns out Karl has a gift for physical comedy and is a welcome match for Chenoweth in their scenes. Both of them manage to be somehow wacky and restrained at the same time. Together, they are fizzy and fun.

This is the first time "On the Twentieth Century," written by Betty Comden and Adolph Green with music by Cy Coleman, has been revived since it debuted in 1978, and it's clear why. Though it's gorgeous to look at, it doesn't quite hang together; it certainly isn't a classic along the lines of Comden and Green's  "On the Town" or "Singin' in the Rain," or Coleman's "Sweet Charity." There's no bite here and not much heart, either. Luckily, Chenoweth's performance brings both. She fires up the engine of the show and brings it smoothly into the station.