As a mysterious epidemic grips the idyllic Riviera, the French authorities turn to the brilliant mind of Dr. Petrie for answers. Meanwhile, a bewitching siren named Fleurette captures the attention of Alan Sterling, leaving him entranced by her enigmatic allure. But when Petrie's laboratory reveals the presence of a deadly combination of sleeping sickness and plague, the renowned Sir Denis Nayland Smith is summoned to unravel the truth.
