On the day of their to England with the authentic Mocana relics Sir Lionel Barton hurries his niece off to Greywater Park, his Norfolk estate to prepare for her wedding to Sean Greville. Greville, meanwhile remains in London in Barton's townhouse in charge of the relics and to keep an appointment the following morning with a group of orientalists who are coming to examine them. That night Greville's memory covering a blank period of several hours is restored to him through a drug given to him by Fa Lo Swee, Fu Manchu's daughter. 

Upon the arrival of the orientalists it is discovered that the relics are not the authentic ones but the imitation ones...