The story is about a boy named Kalle Blomkvist who with his friends solves crimes. But also play the battle between the red rose and the white rose with his rival friends. But everything changes when Kalle Blomkvists friend finds a dead man in a cabin and then must his friends and he find the murdurer.

An engineer and his 5-year old son Rasmus are kidnapped by a group who wants to get their hands on the engineer's latest invention. Three kids become witnesses to the kidnapping and decide to follow the kidnappers to an island and attempt to make a rescue.