Sanne (Hanna Obbeek) loves stories about ghosts and other mysterious things. Her father Lucas, is a famous ghost hunter. During a holiday Lucas is asked to chase ghosts of the former cruise ship 'Rotterdam'. Sanne is very happy to hear she and her little brother Thomas can come along. On the ship she meets ghost Bobby (Nils Verkooijen), a boy of her age, who has been wandering the ship since the sixties. Sanne decides to help Bobby.

The fourth movie about the popular teacher Mees Kees.