It is 1502 and Arthur Tudor has just married the Spanish infanta Katherine of Aragon, solidifying the alliance between England and Castille, when they are both struck down with the infamous sudor anglicus, better known as the sweating sickness.
In the history books as we know it, fifteen-year-old Arthur succumbs to the illness, leaving Katherine - and England - at the mercy of Arthur's younger brother, the future King Henry VIII.