Charley Wyckham and Jack Chesney pressure fellow student Fancourt Babberly to pose as Charley's Brazilian Aunt Donna Lucia. Their purpose is to have a chaperone for their amorous visits with Amy and Kitty, niece and ward of crusty Stephen Spettigue. Complications begin when Fancourt, in drag, becomes the love object of old Spettigue and Sir Francis Chesney.
Sir Fancourt Babberly, known affectionately as Babbs, is a student at Oxford University. Two of his friends, Charley and Jack, who wish to propose to their sweethearts, invite the girls to lunch, promising them that Charley's aunt will be present as chaperon. The aunt, Donna Lucia, does not arrive, and Babbs (who is costumed for a student theatrical in which he has the part of an old woman) is pressed into service to impersonate her. Mr. Spettigue, the girl's guardian, unexpectedly shows up, as does Jack's father. Both men flirt with "Charley's aunt," believing her be a woman of great wealth. Donna Lucia then appears but conceals her identity. By accepting Spettigue's proposal of marriage, "Charley's aunt" gains his consent for the two girls to marry Jack and Charley. Babbs then reveals himself; he becomes engaged to his own sweetheart, Ela; and Jack and Charley become engaged to their respective sweethearts.
