Everyone in Valleby is looking forward to Valleby Day when a thief suddenly strikes and carries out a series of thefts. The thief leaves behind symbols linked to the zodiac and space. The thefts seem to be aimed at ruining Vallebydagen. Lasse and Maja throw themselves into the case and engage the grumpy master thief Lillie Ragnarsson as master mind in the investigation, which soon develops into a cat-and-mouse game where the thief always seems to be one step ahead.
But who really is this cunning master thief and what is his motive? Will Lasse and Maja manage to crack the riddle and stop the thief before the entire Valleby Day is cancelled?
