Denise de Flavigny, a young convent student, discovers a double-life of the organist Célestin, who teaches her music at the convent. He secretly composes popular operettas for his mistress Corinne. Célestin visits the city to witness the premiere of his latest effort; Denise escapes the convent as well. Following a quarrel with Célestin, Corinne walks out and instead, Denise appears in her role, taking the name Mamzelle Nitouche. Denise falls in love with Fernand, a handsome young soldier. Both Denise and Célestin are mistaken for soldiers absent without leave and shipped off to an army camp. A series of coincidences brings happiness to all concerned.