It's 1944, and two young Canadian able seamen, Glen Cassley and Arthur "Ding Dong" Bell, find their ship sinking beneath them after a German submarine unleashes an acoustic torpedo. Miraculously, everyone on board survives, and Glen shouts out triumphantly:

"You know what this means, Ding? Survivor's Leave. We qualify for Survivor's Leave!"

With fun and adventure on their minds, Glen and Ding set off for London. But there is no rest from battle, for the Germans have begun dropping a new kind of bomb, the horrific V-1s, or doodlebugs. When a neighbour and her baby are trapped under their collapsed and burning home, an injured Glen is on the frontlines.

Glen and Ding then accept an offer to travel to Cornwall where they are to stay in a rundown manor house, Penraven. Their stay turns out to be more exciting than the boys could have imagined. Built atop a cave-riddled cliff, Penraven has been the home of smuggling, murder, dungeons and ghosts. To add to the excitement, the boys meet two young English girls who turn out to be charming company!

But the young seamen soon discover that sinister forces have an interest in what lies hidden below Penraven, for the Nazis have hatched an unprecedented scheme involving biological warfare, and it seems the caves are the perfect place from which to set the destruction in motion.