ACT I
Man in Chair - a mousy, agoraphobic Broadway fanatic - decides to cheer things up by playing a record of the 1928 musical, The Drowsy Chaperone. As we listen, the characters of The Drowsy Chaperone come to life in his apartment! ("Overture")
Mrs. Tottendale, an absent-minded dowager, is hosting the wedding of showgirl Janet Van De Graaff and oil tycoon Robert Martin. A barrage of characters arrive ("Fancy Dress"), including Underling, the butler; George, the harried best man; Feldzeig, a vaudeville producer; Kitty, a ditzy, would-be showgirl; two Gangsters disguised as pastry chefs; Aldolpho, a Latin lothario; Janet's Drowsy (i.e. tipsy) Chaperone, and Trix, a glamorous aviatrix.
Feldzeig agonizes over Janet leaving showbusiness. The Gangsters, in the employ of one of Feldzeig's investors, pressure him to sabotage the wedding.
Robert and George nervously prepare for the wedding ("Cold Feets"). George suggests that Robert blow off some steam by roller-skating, and blindfolds him to prevent Robert accidentally seeing the bride before the wedding.
Feldzeig begs Janet to reconsider the wedding, but she rebuffs him ("Show Off"). Feldzieg enlists the help of Aldolpho to seduce Janet and sabotage the wedding.
Janet shares her excitement with her Chaperone. This prompts the Chaperone to perform a rousing anthem ("As We Stumble Along"), which isn't particularly relevant to the plot. Aldolpho arrives and, mistaking the Chaperone for Janet, seduces her ("Aldolpho").
Janet encounters Robert, who is blindfolded and roller-skating. Robert fails to recognize her because she is pretending to be a French girl. They relive the moment ("Accident Waiting to Happen"). This results in a kiss, whereupon Janet accuses Robert of infidelity.
Kitty fails to persuade Feldzeig to let her replace Janet. The Gangsters are angry that Feldzeig has not ruined the wedding. He distracts them by convincing them that they have talent ("Toledo Surprise"). Aldolpho announces that he has seduced the bride, but Feldzeig informs him that he has seduced the Chaperone. Janet announces that the wedding is off. ("Act I Finale")
ACT II
Janet laments the collapse of her romance with Robert ("Bride's Lament").
Mrs. Tottendale assures Underling that the wedding preparations should continue, regardless of the apparent disaster ("Love is Always Lovely").
The Chaperone informs Janet that she and Adolpho will marry. Mrs. Tottendale and Underling announce that they also plan to marry. Robert asks Janet to reconsider. She confesses that she was the French Girl, and agrees to marry. Feldzeig is saved from the Gangsters by his new leading lady, Kitty, and they become engaged.
George forgot to arrange for a Minister, but, fortunately, Trix the Aviatrix arrives, and it is decided that she can officiate the weddings ("I Do, I Do in the Sky").
The show is abruptly cut short by a power failure in Man in Chair's apartment. He explains his love for the show as an antidote to sadness. The cast joins him for the grand finale ("Finale Ultimo").
