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In Paris Maria Gambrelli, Mr. and Mrs. Benjamin Ballon's French parlor maid is accused of killing her Spanish lover.  Inspector Jacques Clouseau, accidentally assigned to the case, believes her innocent despite all the facts indicating that she is guilty.  Dreyfus, Clouseau's superior, removes him from the case and arrests Maria, but, on the following day, Dreyfus learns that certain influential people wish Clouseau back on the case.

Reassigned, Clouseau releases Maria and before long finds her with the gardener's dead body.  Again arrested for murder, Maria is quickly released by Clouseau, who still believes in her innocence.  He follows her to a nudist camp where Dudu, the Ballon's first maid, is found murdered and Maria again comes under suspicion.

Lafarge, the Ballon's majordomo, is then murdered.  Maria is once more arrested, and Clouseau is again removed from the case.  Dreyfus reassigns the case to Clouseau, who releases Maria and takes her nightclubbing.  In the course of the evening, four innocent people are killed, around the oblivious Clouseau, as a result of unsuccessful attempts on his life.

The inspector gathers the six remaining suspects in the Ballon house.  They begin to accuse one another until the lights go out, and Maria and Clouseau find themselves alone.  All six attempt to flee in Clouseau's car, which has been wired with a bomb intended for him.  The car explodes and Clouseau has, in his own way, solved the case by the elimination of the suspects.  Dreyfus goes insane because he is the real murderer, having committed the crimes to discredit the bumbling detective and thereby remove him from his staff, only to have him emerge a hero.