An ex-nun, Mary Appalonia, is scared during a black-out by a person in a black ski mask, looking through the reporter's briefcase. Afterwards, the student, Mary Evans is abducted through a secret passage behind the bookcase while the reporter is in the room. He tries to investigate, as he did not see, and then is apprehended himself. The actress, who plays Mary in Mary, Mary Quite Contrary, A TV show, sees and screams. Inside the passageway, the reporter is found dead. He had been Mary in the Just Ask Mary column of the New York Times. Mary Evans is found passed out.
The Mary Murderer is one of the people on the bus. But suddenly, the handyman for the nuns finds a man in a black ski mask outside. It's Mary Evans' boyfriend, who she'd had a fight with. He had come to apologize. He is grilled by the policeman in the kitchen but found as nothing. Later that night, Miss Evans calls the policeman into the front room. She recalls a letter dated 7 months back from a Mary that complained of an outrageous husband who she feared who was a cop. The policeman snaps, as he is the murderer, and tries to strangle Miss Evans. He's stopped by a suit of armor, in which, an undercover officer acting as another Mary, Mary Adams in fact, had hidden. She knocks him out with a broad sword and explains the rest.
In the end, Miss Evans is asked by her boyfriend to be married.
Most of the comedy in this revolves around simple puns and misuse of words through most of the Marys, especially the elderly nun, who exclaims that "I can quit! I didn't know we could quit!" and believes that decaf coffee is made of baby cows.