Ondina es una historiadora que enseña sobre el desarrollo urbanístico de Berlín. Cuando el hombre al que quiere la deja, un antiguo mito se apodera de ella. Ondina debe matar al traidor y regresar al agua.

When Willi's father is abducted and is only released for a valuable statue from his art collection, Tim is the only one who believes Willi that the police are on the wrong track. Together with the smart policeman's daughter Gaby and the highly intelligent outsider Karl, they start to investigate on their own. Against all odds the four discover a conspiracy. In the course of their first big detective adventure they grow together into a committed community, and so Tim, Klöschen, Karl and Gaby become the band TKKG.