Fu Manchu's Bride by Sax Rohmer

As an epidemic swees the Riviera, French authorities call upon Dr Petrie to find an answer. During this crisis, a mysterious siren on the beach captivates Alan Sterling. She tells him her name only—Fleurette—and flees. When Petrie’s lab cultures reveal sleeping sickness and plague, Sir Denis Nayland Smith is summoned. Soon their investigations leads to Fleurette—and Dr Fu Manchu!