One day, Grandpa Jeremi causes such chaos in the nursing home that he is threatened with being transferred to a psychiatric hospital. Marta, his daughter, agrees to take him in, although it is difficult for her, because Jeremi is unpredictable and has a vivid imagination. The situation is complicated by Jagoda, Marta's daughter, who adores her grandfather and shares his crazy ideas. When Jeremi refuses to move in with the family, Jagoda decides to take matters into her own hands. The girl and Grandpa set off on an adventurous journey to the legendary ship Światło Morza. A gang of villains led by the rich man Waldemar and Jagoda's terrified mother set off in pursuit of them. And a dragon - a dragon sets off after them too.