Klaus Gremme, a retired instructor with the combat swimmers at the Baltic Sea, sets off for Lake Constance to meet his son Thomas and his grandchildren. They don't know anything about him because Klaus left his wife and Thomas when the boy was still very young. Klaus takes up residence with Mona, a single mother whose house is across the street from Thomas'. The reunion with his son turns into a fiasco, but Klaus doesn't give up and develops an elaborate plan to win Thomas and his family over after all. In the coming weeks, however, the ex-fight swimmer constantly clashes with his esoteric, pacifist landlady Mona. She and her children, the overweight Linus and Claire, who has Down syndrome, slowly grow fond of the lone warrior. In the end, the rapprochement with his own family seems to have failed. But Klaus may have found a new, completely different family in this search.