The family's long awaited vacation at the Wadden Sea is threatened by the fact that Father is suspected of being a burglar. The family does everything to prove his innocence - but Father's unfortunate actions make him look more and more suspicious in the eyes of the rooms. Finally, Little Per must do something illegal to find the right thieves. But it is about to go wrong and suddenly the whole island is convinced that Father is guilty and that the family must be away from the island. At the last minute, Lille Per finds the decisive track in the search for the right thieves, but even that doesn't succeed. So the whole family has to get together in a wild plane to make sure the thieves don't get away from the island.