 In a French provincial town, Michel Delassalle, a sadistic headmaster of a school belonging to his wife Christina, a fragile young woman with a weak heart, carries on an affair with Nicole Horner, a strong, forceful teacher who has been his mistress from the day she arrived. He has, however, treated her as badly as his wife, and the two women have been driven into an alliance against him. Together they work out an elaborate plan to rid themselves of their common tormentor. Luring him away from the school to Nocole s cheap lodging house, they induce him to drink some doctored whiskey - and drown him in a bath. The body is later wrapped in a nylon tablecloth, packed into a laundry basket, taken back to the school, and at dark tipped into the grimy water of the school swimming pool. When, shortly after, the pool is drained, watched in anguished expectation from a window by the women, no corpse is there. Soon other mysterious events begin to occur...