The three boys are still aboard the St Valery with Barry when she gets hijacked after leaving the Namibian port of Luderitz. The hijacker is a young German, by the name of Gustav Stoltenhoff, who has just joined the yacht for the final leg of the journey to Cape Town. He is desperate to reach the tiny South Atlantic island called Inaccessible in the Tristan da Cunha Group.Gustav is a descendent of one of the few people ever to live on Inaccessible Island, and he has recently learnt that a German U-boat put into the island late in World War Two on its way to find refuge in Argentina. Aboard the submarine was a treasure of artworks looted by Hermann Goering.After the treasure has been loaded aboard the St Valery in a secret cave, following their hazardous ocean crossing, the three boys and Barry are marooned on the island. In their attempt to get rescued, they encounter most of the island's amazing bird population - albatrosses, spectacled shoemakers, the tiny Inaccessible rail, rockhopper penguins and the vicious skua.