Grandpa Oskar takes neither the truth nor himself very seriously. The rascal has just been released from prison, where he was serving a sentence for imposture. Since the ex-con needs a place to stay, he quartered himself in the old construction trailer in the farthest corner of the garden of his daughter Tilda, who is still mad at him. The senior soon meets his autistic granddaughter Fanny, whose antics and peculiarities threaten to break the family under. In contrast to the old man, the 8-year-old takes the truth very seriously. In order to gain their trust, Oskar does not introduce himself to the comic-loving girl as the criminal grandpa, who has been missing for years, but as Professor Krypton. For Fanny, who prefers to wear a brightly colored superhero costume and is teased at school for it, the omniscient mentor from the Superman planet comes along just at the right time, because she has a dream: To win the talent competition at school!