Take It Adam (1989)

Adam has a hard life. His wife cheats on him and he can't find a job. Then his wife gets him a job as a private detective at her friend's company. There he is put on the case of Bert's wife, who is Adam's wife's lover. When Adam enters Bert's house for the purpose of observation, he gets lost on the floor and thus catches Fanny, whose husband is in the process of screwing Bert's wife. The entanglements get wilder and wilder and in the end the cheaters are the cheated.