Finally the summer vacations are here, which Flo has been waiting for so long. And this time he doesn't let himself be talked out of spending it with his dog Lassie. So he lets his parents fly to Gran Canaria on their own and takes himself to the mountains in South Tyrol with the housekeeper Gerhardt. Aunt Cosima has her farm there, where she spends her life together with her two foster children Kleo and Henri and the dog Pippa. Gerhardt himself finds lodgings at the Grand Hotel Sternberg, where he helps out the owner, Bianca Sternberg. Everyone is thrown into a tizzy when burglars gain access to Aunt Cosima's farm and steal Pippa. But the thieves have made their reckoning without Lassie, who immediately sets off in search of her canine friend...