Debra Monk infuses Mrs. Miller with a sweet, old-fashioned optimism and naiveté (Photo by Margot Schulman)

Long before there was William Hung, there was Mrs. Miller.

While performing acts didn’t exactly go viral in 1966, a similar frenzy embraced the unlikely and true success story of Elva Ruby Miller. The sweet, naive woman at the center of Signature Theatre’s Mrs. Miller Does Her Thing couldn’t sing to save her life, but she was the last one to know it.

After driving her church choir companions crazy and spending her husband’s money on vanity studio sessions, Miller was thrown together with a group of chipper backup singers and jingle recorders. A producer urged Miller, who normally spent her time massacring religious songs, to record Petula Clark’s “Downtown” as a lark with the trio singing back-up. The amusing but cringe-worthy recording caught the attention of another, more seasoned producer, who turned Miller into a four-album phenomenon. But was she in on the joke?

Debra Monk infuses Miller with a sweet, old-fashioned optimism and naiveté (“Are you from Europe?” she asks a producer when he dares to kiss her hand). She makes her audience collectively hold its breath anytime someone might tell her that her fans are mocking her. Marquee director (and frequent Stephen Sondheim collaborator) James Lapine has a few clever tricks up his sleeve, like shifting the lighting and allowing Monk to slip into a pure, pristine singing voice on occasion to represent what Mrs. Miller must hear in her own mind when she performs.

Mrs. Miller initially takes the audience along for a zany, endearing ride, as her journey brings her everywhere from The Ed Sullivan Show to Vietnam to perform as part of Bob Hope’s USO tour. It’s a treat to watch the same jingle-singing trio surround Miller with goofy, overly enthusiastic choreography for her stage act.

But Vietnam casts a shadow over Miller. Contemporary youth were unlikely to embrace a figure who supported an unpopular war, and the draft caught members of her own family in its clutches. The people surrounding her worked to take her act in an edgier direction in a desperate ploy to maintain her success. Then there’s the matter of Mr. Miller (Boyd Gaines), stuck at home recovering from a stroke, growing resentful and abandoned as his wife takes a whirlwind tour surrounded by those he believes are taking advantage of her.

Mrs. Miller is a delightful production that isn’t afraid to get a little real. Though its sobering late-act turn can feel abrupt at moments (one character expresses her own social awakening in about three minutes of dialogue), it also brings a sincerity and heft to a fizzy, fun show. A late-in-life interview shows a formidable woman taking stock of her life in a way that reveals no one really should have underestimated her in the first place — even if staying on-key and “blending” with the crowd was never her strong point.

Mrs. Miller Does Her Thing runs through March 26 at Signature Theatre. Tickets ($40-$99) are available here.