The Olsson family move into a castle that turns out to be haunted. The kids, with their dim parents oblivious to all the strange things that are happening, are caught in the middle of a big mystery in the centuries old castle.
Rasmus lives at an orphanage. He's OK, but wants a mom and a dad, and from time to time some comes to find a child, but they always chose little girls curls. Rasmus realizes he has to run away and find parents himself.
The Melkersson family decides to leave the city for the summer to rent a house in the Stockholm archipelago. They come to enjoy the simple life there and all adventures that come their way together with resident family, the Grankvists.