With UA’s new musical “City of Angels,” I had a mystery on my hands. Sure, its 1940s Noir parody had a convoluted detective story, but this mystery didn’t involve a millionaire’s missing daughter or blackmailing mobsters – it was the case of who killed the audience.

Don’t get me wrong, “Angels,” the department’s second musical farce in a row, is funny. In fact, it’s a riot. Larry Gelbart’s book slops on equal helpings of razor-sharp wit and schmaltzy hardboiled pulp as he tells the stories of Stone, a fictional private eye hunting a missing heiress, and Stine, the persecuted writer bringing Stone to the screen for 1940s Hollywood – all illustrated by a jazzy, big-band, lounge-lizard score.

So, why did I feel like I was watching “Purgatorio” again?

When Stone freezes in the middle of a monologue as Stine gets writer’s block – crickets. When Stone says, “LA. Not much different than a pretty girl with the clap” – crickets. When a group of cops transforms into a Mexican mariachi band as they beat Stone up…well, that got a chuckle.

At one point, I leaned over to my date and whispered, “What the heck is wrong with this crowd?”

Last semester, the audience was in stitches with “Flora the Red Menace,” and “Angels” is basically what we would get if last spring’s “The Realm” knocked up “Flora” at a cast party. But while that show was a big, colorful, Vaudeville beach ball, director Karen Baker keeps “Angels” subdued, opting for the sort of finesse the tiny Allen Bales allows.

Musically, it works. “Angels” lacks “Flora’s” boisterous production numbers, instead favoring duets, charm ballads and a slick lounge piece by Jessica Berzack that takes full advantage of the Bales’ intimacy. Plus, David Zippel’s lyrics are often as clever as Gelbart’s book, especially in Stine and Stone’s Act I climax “You’re Nothing Without Me.”

Admittedly, Gelbart’s wit could have used a little more animation. While the exaggerated grizzle of Michael Luwoye (who already took hardboiled for a spin in “The Realm”) is just right with Stone, Russel Stephens’ unassertive, brooding Stine doesn’t show much passion for his writing. Cooper Kennard’s pompous director Buddy makes a wonderful loudmouthed foil, but Stine has a lot of his own bite Stephens doesn’t quite bring to life.

The set is full of elegant, modular art-deco bits that, paired with some clever lighting, make interplay between brooding Noir L.A. and sunny Beverly Hills almost seamless. But, of course, one constant presides over both worlds: a gigantic sign reading HOLLYWOOD.

But the design was harder to appreciate from my seat, which was to the side of the Bales’ thrust stage. Until I could change at intermission, I missed a lot of sight gags and saw a lot of back. A dame in her underwear tries to woo Stone: The audience in front got a graceful and seductive dance number. I got a view of a glowing mic-pack that blinked green when she hit the high notes, like if the Bionic Woman worked at a strip club. Head for the center, if you can.

So, what killed the audience? Who knows, maybe I just came on a bad night. Maybe the house just had a severe case of the Mondays. For all I know, the Wednesday crowd could be in tears as I write this. Go to “City of Angels.” It’s fun and cool. But if you go, give it a chance. Don’t be afraid to laugh, even if you’re the only one.