A kidnapping. A map. A lost u-boat. There is something fishy going on in Paris. The kidnapping of journalist Pierre Martin seems to be connected to a marine expedition to the island kingdom Sitomeyang on the other side of the globe. Clues point to the mysterious organisation The Octopus, whose tentacles reaches everywhere. Only a band of intrepid troubleshooters can find out how all of this is connected and solve the U-Boat Mystery.