The China Seas, 1805. Travelling on a vessel about to be shipwrecked is Xavier Balmis, a visionary Spanish doctor obsessed with a mission that many consider madness: to take the vaccine for smallpox to China inside the bodies of orphaned children and so halt the advance of the most fatal disease known to man. However, his brave mission is in danger: fearsome Chinese pirates surround them, the country’s authorities refuse any western interference, and Tomas, the last of the orphans who Tomas is using to convey the vaccine, has disappeared. Only when the emperor’s nephew falls victim to the disease will Balmis obtain permission to carry out his plan to vaccinate the population and prevent the Empire from disappearing, but the cure depends on the life of a single boy...