The rival gangs of the White Rose and the Red Rose are locked in a struggle for possession of the magic stone. The Red Rose gang has the upper hand. When Kalle, Anders and Eva-Lotta of the White Rose gang are out and about one night in search of the magic stone, they witness the kidnapping of the professor and his little son Rasmus. The professor has developed a formula for a bullet-proof metal which is apparently stored in his house. Eva-Lotta stows away in the kidnappers‘ car and lays a trail for Kalle and Anders to follow. On a deserted island, the kidnappers try to make the professor reveal where the formula is hidden, but he refuses to tell. His five-year-old son is more talkative. Thank goodness master detective Kalle is nearby…A new film version of Astrid Lindgren’s famous novel for children.