Flo (Nico Marischka) is twelve years old and the Collie female dog Lassie, is his best friend. Since he can think, he and his faithful dog live in a quiet village in southern Germany. But one day Florian‘s father Andreas (Sebastian Bezzel) loses his job, which leads to the family having to move to a smaller apartment where Lassie can no longer live because no dogs are allowed there. It almost breaks Flo’s heart. Lassie finds a new home with Graf von Sprengel, who immediately sets off on a holiday at the North Sea with Lassie and his granddaughter Priscilla. But there Lassie isn‘t treated well by the sneaky janitor. When the opportunity presents itself, Lassie tears herself apart and begins an adventurous journey across Germany, always in search of Flo. But Lassie is not the only one who sets off on a journey. Flo also can‘t stand it any longer and starts a search for his dog. It won‘t be easy to get the duo down!