During their sailing holiday, Heleen and Jelle come into conflict with game warden Kees van de Wal in the bird breeding area. After spying on smugglers at night, their boat is cut loose. They get into trouble with gold smugglers and are sailed over. Finally, they unmask the perpetrators who are trying to salvage a gold treasure from the Second World War at Vredenhof, a cemetery for nameless drowning people.