PRAY SHE STAYS ON KEY: Neva Rae Powers and James Valcq are singer and accompanist in Souvenir. Credit: Courtesy American Stage

PRAY SHE STAYS ON KEY: Neva Rae Powers and James Valcq are singer and accompanist in Souvenir. Credit: Courtesy American Stage

The astonishing truth is that there really was a Florence Foster Jenkins. From about 1932 to 1944, this irrepressible socialite, who couldn't hold a melody, gave yearly concerts at New York's Ritz-Carlton Hotel and even sold out Carnegie Hall with patrons who came to laugh at her famously undependable soprano.

Accompanied by pianist Cosmé McMoon, she made successful recordings — you can find a few cuts on YouTube — and never seems to have noticed that "Caro Nome" and "Ave Maria" were hopelessly out of her range. Throughout her whole bizarre career, it didn't occur to her that she was more joke than legitimate star or that the laughter with which her recitals were greeted was prompted by something other than professional jealousy. She was ignorant and blissful.

Now American Stage is bringing us Souvenir, Stephen Temperley's charming musical play about Jenkins, and it is delightfully silly and affecting. Using only two characters — Neva Rae Powers as Jenkins and James Valcq as accompanist McMoon — Temperley takes us through the start of Jenkins' career all the way to the final Carnegie Hall concert where she might have glimpsed, however briefly, the truth about her notoriety.

Souvenir offers two kinds of music: McMoon's attractive, jazzy saloon crooning and Jenkins' all-out assaults on Mozart, Gounod and Strauss. You might think that the spectacle of a woman singing off-key would get old after a few tunes, but actress Powers always brings something original to each disaster, whether a ridiculous outfit, certain unconsciously vulgar gestures or just an innovative screech where a high F should have been. And Temperley brings us the Jenkins story not through her own eyes but through those of McMoon, a sensible, compassionate narrator who comes to love Jenkins and — almost — respect her.

It's fun to follow the Jenkins story from McMoon's perspective: He's never cruel — and is sometimes remarkably tender — and he's as baffled by the Jenkins phenomenon as we are. His piano-playing, whether backing Jenkins or himself, is always of top quality, and his renditions of popular standards — from "One for My Baby" to "It All Depends on You" — make a nice counterpoint to the arias that Jenkins repeatedly mauls.

Strangely enough, Souvenir seems aimed especially at music lovers: If certain later recordings of Maria Callas have put you on edge, this play will take you over the cliff, leaving you laughing all the way down. You may even find yourself asking — as McMoon does in Act 2 — if Jenkins' performances weren't really clever comments on "our assumptions of what music is." Hey, who made the rule that one has to sing the notes as written?

When the play begins, McMoon has been spending five years writing art songs, playing piano for voice teachers and rehearsing the pieces he would have played at recitals — if anyone had asked. When Jenkins' nephew tells him that his aunt is seeking an accompanist, McMoon is ready to try something new. He listens to her decision to "scale the pinnacles of the soprano repertoire" and is particularly responsive when she mentions her commitment to pay him "commensurate with your dignity."

Then she begins to sing — or rather screech — an aria by Verdi, and McMoon is stunned, frightened, perplexed: "Was I in the presence of mere delusion or a kind of dementia?" More bad singing brings more confusion, and finally he manages to tell her that "I'm hearing a certain want of … accuracy." Jenkins is bewildered: what inaccuracy? She has perfect pitch, he should know, and anyway, she's not taken in by the "modern mania" for precision.

McMoon is eventually touched. He sees that she believes in herself "the way a child might believe," and he begins to feel protective. And then there's that little problem of paying the rent. He agrees to accompany her for one concert only. Which becomes another. And another. And no matter how badly Jenkins sings, the audiences love it and demand more. McMoon understands why: He sees "them crying. When she sang. Doubled over in their seats. Hitting each other, convulsed. There were gasps, sudden shrieks. They'd jump to their feet and run up the aisles. You'd hear doors banging. And the sound from the lobby of people laughing … You see a lot from a piano bench."

It becomes his hope that Jenkins will never see it all as he does. He has come to guard her innocence.

If the tone of Souvenir is set by the compassionate McMoon, the comedy is squarely in the hands of Powers, and she wields it capably. Powers' Jenkins is a wonderfully obtuse society woman, incapable of hearing the foul noise she makes or of understanding the cruel logic that brings sellout crowds to her concerts. Not recognizing that she's making a fool of herself, she carries herself like a much-beloved diva, a woman whose special virtue it is to treat the besotted crowd as her equal.

Wearing ridiculously emblematic costumes designed by Adrin Erra Puente, she clambers around Frank Chavez's attractive set with the sangfroid of a woman who just knows that her every movement is, from the audience's standpoint, delicious. Director Steven Flaa gives Powers little gestures that add to the comedy: the readjusting of an angel's wing, the discovery of a hair in her mouth, a little backward kick when she's trying to illustrate a Mexican theme. The result is often hilarious. And there's a surprise at the show's end that is exceedingly satisfying.

So if you want a few good laughs — and a musical history lesson besides — see Souvenir. It's one of the most pleasant comedies I've witnessed in many years, and the American Stage production is first-rate. Florence Foster Jenkins brought a lot of joy to a lot of people 70 years ago, and now she's doing it again.