Lawyer Arnold König has just moved into a new house in Bonn with his family. On his first day at work, Felix the apparently stray St. Bernard runs into his car. While the stressed-out Arnold vehemently resists keeping the dog, his wife Ellen and children Julia and Tim immediately take him to their hearts. But that soon changes. Chaos soon breaks out in the König household when the curious Felix explores his new home and turns the whole house upside down. From now on, the Königs are no longer safe from surprises. Freshly planted flowerbeds are razed to the ground again. The neighbor's cat is chased off their property in wild chases. The specially built doghouse soon falls victim to the dog's temperament and Felix doesn't even stop at the fridge at home. Despite everything, the Königs can't do without their faithful St. Bernard.