12-year-old Mariana and her stepbrother Marcus end up in a home-built rocket. Behind the rocket construction are Albert, a slightly crazy scientist, and his helper Lemming, a talking lemming.

Rymdresan

A new family moving into Greveholm Castle. The plot takes place sixteen years after the original "Mysteriet på Greveholm". The Olsson family has now moved from the castle and left the ghosts Jean and Staffan, who have lived alone at Greveholm since then. The castle has been dilapidated for some time. One when a new family moves into the castle, the ghosts are happy to finally have some company. The ghosts want to do everything for the family to feel comfortable in their new home. However, it soon turns out that the castle harbors much bigger secrets than anyone previously thought.