Biggles and the team help Raymond out in a search for Nazi gold in the southern ocean (around Kerguelen Island). The title refers to this being their second case in the Air Branch of the CID.

A German submariner is shot trying to get a message to British Headquarters in Germany. His dying words tell of a missing U-Boat returning to the Southern Ocean to pick up a stash of stolen Allied gold from its secret base. Biggles and the team de-camp to Kerguelen Island to try and locate it and retrieve the gold for HM government.

This they manage to do (of course), but not before the usual litany of narrow scrapes, missing teamsters, etc. At one point Biggles and Algy are saved from a firing squad by Ginger firing a whale harpoon!