In the tenth Wallace Boys series, Nigel and Bruce have been given an assignment by the Foreign Office of the United Kingdom. They have to try to help the faltering monarchy of the small Alpine Kingdom of Ruritania on the verge of a coup, the Wallace Boys find themselves in a desperate search for gold and art treasures taken from the fabulous Schloss Falkenstein and hidden in a remote mountain lake by the Nazis at the end of World War Two. To do this they must team up with the Crown Prince, the Archduke Karl-Franz; get the help of a band of gypsies; climb a glacier at night and paraglide down to the lake. But there is a deadline which is drawing dangerously near. Can they make it in time?