Hugo Brinkmeyer is a rather obsessive tax accountant, with not much of a personality outside his work. His long-suffering wife Gerda sometimes finds him difficult, and they have no children. Leaving a club together one night, he takes the wrong hat with him. Eventually tracing the owner, so as to get his own back, the other man (Schwidders) asks his advice about his own tax affairs; he reveals that he has twin sons by an extra-marital affair, and his wife doesn't know. Can he nonetheless get tax relief for them? He takes Schwidders' papers with him agreeing to see what can be done, and goes on to a birthday party of an old school friend, Süsskind. It's in another club, and he stays longer than he should, and drinks more than he should. Late at night the club owner asks him for help with the accounts, and Brinkmeyer agrees, and stays even later going through the books, and drinking, with help from a dancer, Rita. When he gets home his wife cold-shoulders him, and he is in big trouble; he then discovers that he has brought the wrong briefcase home from the club ... Schwidders' papers about the twins have been left behind, and all he has is the negligee of Rita; evidently she keeps these garments in her briefcase. Schwidders is not pleased that his secret affair might be exposed and Brinkmeyer tries to sort matters out. When he is at Schwidders' office, the mother of the twins unexepctedly brings them in, and to avoid his secret getting out, Schwidders says they belong to Brinkmeyer, and he is lumbered with them for a day. He doesn't go to work, which earns him no credits with his boss or his wife. How will he put matters right?