This time Fu Manchu and his army of henchmen are kidnaping the daughters of prominent scientists and taking them to his remote island headquarters. Instead of asking for ransom, Fu demands that the fathers help him to build a death ray, which he intends to use to take over the world. But Fu's archenemy, Nayland Smith of Scotland Yard, is determined not to let that happen.

Grisly strangulations in London alert Nayland Smith of Scotland Yard to the possibility that fiendish Fu Manchu may not after all be dead, even though Smith witnessed his execution. A killer spray made from Tibetan berries seems to be involved and clues keep leading back to the Thames.

A British colonial policeman in Africa investigates a murder in a hospital up river.

A former district officer is assigned to work on a team of diamond prospectors, who are busy double crossing each other until they are blown up having found bullion.