A naval officer who had deserted several years earlier is drawn back to the Navy when World War II begins. He re-enlists under an assumed name, and is assigned to a minesweeper, where he has to perform hazardous duties while at the same time keeping his real identity a secret.

Captain Drummond is travelling to Switzerland to marry his girlfriend. However, when a cargo containing dangerous explosives goes missing from its place, Drummond is forced to delay his plans.

Drummond's girlfriend is kidnapped by his enemies and he along with his friend Nielsen, an inspector from Scotland Yard, follow the trail and try to rescue her from the kidnappers.

Drummond manages to save a woman from jumping in front of his car but she runs away with his car. He traces her and she asks him to help her out of a dangerous situation.

In the midst of World War II, Sherlock Holmes rescues the Swiss inventor of a new bomb-sight from the Gestapo and brings him to England, where he quickly falls into the clutches of the evil Professor Moriarty.