Star Surgeon — James White

Trying to solve the baffling medical problem of the comatose, immortal, and possibly homicidal demigod Levellin would have been trouble enough for Senior Physician Conway. But the episode triggered the gravest crisis in the history of Sector General. For when the alien enlisted Conway's help in healing the entire, plague-ridden population of a shadowy Empire, the star surgeon found not just disease, but a monstrous corrupt plot against an entire planet.