Lucille is threatened with marriage to a man she doesn't want. Her cousin, Sabine, plots with her actual boyfriend, Valere, to sneak Valere's valet, Sganarelle into the household in the guise of a doctor. The plan is to trick Lucille's father, Monsieur Gorgibus, into letting Lucille out of the house, where she may rendezvous with her lover and elope. Elaborate hijinx find Sganarelle tasting a urine sample, and, "caught" by Monsieur Gorgibus, Sganarelle masquerades as a twin of his brother, a more respected doctor, and spends much of the play leaping from (and back to) his place on the balcony to the ground level where the "brother" scorns his estranged brother to Monsieur Gorgibus (who has taken the long way down).