At the risk of giving away the ending of “Curtains,” the director did it.

And the choreographer. And the set designer. And the cast. And the writers — two of whom died years ago.

What this gang of merry miscreants did is breathe a faint but nonetheless refreshing blast of air into a format that has been hurting for oxygen of late — the good old-fashioned musical comedy. They may not have gotten away with it entirely, but John Kander, Fred Ebb, and a passel of other pros led by the sure-footed director Scott Ellis have added a harmless new entry into a sadly underrepresented subgenre: the murder-mystery musical.

The setting: a Boston theater in 1959, where a hopeless Wild West musical called “Robbin’ Hood” (think “Destry Rides Again” plus “The Scarlet Pimpernel” minus coherence) is fumbling through pre-Broadway tryout. Among its many liabilities is Jessica Cranshaw, an over-the-hill diva who’s too busy filing her nails on stage to hear her cues. Musicals aren’t easy to fix out of town, but a solution is found for this particular problem: Jessica keels over dead on opening night, the victim of a fast-acting poison.

Who’s responsible? Niki Harris (Jill Paice), the starry-eyed ingenue poised to take the star’s place? Christopher Belling (Edward Hibbert), the egomaniacal director? (“Shall we observe a minute of silence, to match the audience’s response to Jessica’s first number?”) Carmen Bernstein (Debra Monk), the tough-as-nails producer determined to ferry “Robbin’ Hood” to Broadway? What about that likable songwriting team, Aaron Fox and Georgia Hendricks (Jason Danieley and Karen Ziemba), who may actually get to hear their melodies sung in the right key?

Since the entire cast and crew are all suspects, the Boston police force has locked down the theater. Luckily, Lieutenant Frank Cioffi (David Hyde Pierce), the officer in charge, is also the biggest musical-theater nut this side of “The Drowsy Chaperone,” so the investigation routinely comes to a halt as Cioffi turns his attentions to, say, fixing that square-dance number in Act II.

For reasons too complicated and too silly to mention, our hero has 24 hours to salvage “Robbin’ Hood,” solve the murder — along with two others that pop up along the way — and sweep the ingenue off her dainty but suspect feet. This last task is complicated by the presence of Daryl Grady (John Bolton), an amoral theater critic whose lust for Niki and lack of objectivity represent a shameful and scurrilous act of libel on the writers’ part. (Did I mention that Ms. Paice is ravishingly lovely? Objectively speaking, of course.)

The forgettable “Redhead” and “Baker Street” had the genre of murder-mystery musicals to themselves until 1985, when Rupert Holmes struck gold with “The Mystery of Edwin Drood.” Buoyed by a clever gimmick — each audience decided how to end the show, which was based on an unfinished Charles Dickens novel — “Drood” featured Mr. Holmes as composer, lyricist, bookwriter, and orchestrator. He’s back on the case with “Curtains,” but he had some help this time.

The show began life in 1985 as a project for Kander and Ebb, best known now from their long-running revivals of “Chicago” and “Cabaret.” Their original bookwriter, Peter Stone, relished the idea of a backstage mystery, but both he and Ebb died before the project was completed. And so, 22 years later, we are left with a well-oiled hodgepodge of contributions from Ebb and Stone along with Messrs. Kander and Holmes.

As is often the case with long-gestating projects, the number of fingerprints on the “Curtains” script gives several of the gags a musty, humor-by-committee feel. And although a saloon blowout called “Thataway!” is diverting enough, I’m not sure it was necessary to make “Robbin’ Hood” so off-the-charts bad. (William David Brohn’s skittering orchestrations instantly evoke the sound of “Gypsy”-era Broadway.) But the whodunit is a genuine head-scratcher: I went into intermission reasonably content with the show’s musical elements but puzzled by why Mr. Holmes had neglected the murder-mystery angle. It turns out he’d planted a half dozen clues in the first act without my noticing a thing. Maybe the writers have a point about these theater critics.

The score (music by Mr. Kander, who joined Mr. Holmes in supplementing Ebb’s hard-boiled lyrics) largely draws from the brassy, gutbucket sound of “Chicago,” with a clever “Cabaret” in-joke tossed in. And while the score upon first hearing is unlikely to supplant those two Kander-Ebb shows in the public consciousness, two ballads — “Thinking of Him” and “I Miss the Music” — showcase the blithe, confident efforts of old pros at work. In fact, it’s hard not to view the latter song, with one or two swapped pronouns, as a tribute by Mr. Kander (who wrote the lyrics as well as the music) to his professional partner of 42 years:

I miss the music.
I miss my friend.
No need to ask me
What I prefer.
I choose the music
I wrote with her.
I loved the music
I made with her.

While Rob Ashford’s choreography gets cluttered in the “Robbin’ Hood” numbers, he does provide an adorably clumsy ballroom duet for Ms. Paice and Mr. Pierce that conjures the spirit of Fred and Ginger — if by Fred you mean Fred Mertz or maybe Fred Rogers. (Mr. Pierce, whose effervescence and foolproof timing paper over several of the show’s less inspired sequences, has evidently taken some dance lessons since “Spamalot.”)

A proper mystery requires a decent number of suspects, and the challenge is to maximize each character’s brief time onstage. In addition to keeping the pace at a decent clip, Mr. Ellis has packed his cast with a dynamite group of character actors. Mr. Hibbert gets the best lines — “We need a completely new composition, one that’s catchier than pinkeye” — and Mr. Danieley the best song, but Ernie Sabella does the most with the least as Carmen’s philandering husband. Sadly, Ms. Monk is used in virtually the identical capacity (potty-mouthed battle-ax) as she was in the last Kander-Ebb-Ellis show, “Steel Pier.” She once again outshines her material, giving Carmen’s bluster a welcome undercurrent of passion for musical theater, dross like “Robbin’ Hood” included.

Even during its drearier passages, that passion suffuses every minute of “Curtains.” Whether it’s Anna Louizos’s clever, theatre-spanning sets or a “Eureka!” moment as the show-loving sleuth fixes yet another scene in “Robbin’ Hood,” or even a pivotal clue that references 17th-century theater history, the show’s deep-rooted affection for the (literally) wicked stage could bring the lieutenant Frank Cioffi out of any but the most grumbly theatregoer.

Open run (302 W. 45th St., between Eighth and Ninth avenues, 212-239-6200).