A tough detective who is part of an elite New York City unit is trying to find out who killed his partner, but uncovers a plot to kidnap mobsters for money.

Felix Ungar has just broken up with his wife. Despondent, he goes to kill himself but is saved by his friend Oscar Madison. With nowhere else to go, Felix is urged by Oscar to move in with him, at least for a while. The only problem is that Felix is neat, tidy, and neurotic, whereas Oscar is slovenly and casual.