After oversleeping yet again, Alfons manages to catch the bus to his class trip to the Baltic Sea at the last minute. In his luggage: lots of adventure, funny pranks and - wait a minute - his mother's clothes?

The summer holidays have just begun in Brandenburg, but ten-year-old Lea isn’t going to camp this year with her friends as she normally would. One afternoon she spots five boys lifting a large blue oil barrel over the fence of a paint factory and driving away with their loot on a bicycle trailer. Lea's curiosity is piqued. The next chance she gets, she follows the boys and discovers they built a raft on a small lake. The raft is the boys' property and under no circumstances girls are allowed in their gang. But Lea wants to be part of it very badly and takes them up on a dare. Soon summer is full of adventure.