Scattered through the galaxy are thousands of worlds colonized by humans. Many have native microbes dangerous to the human immigrants. Others have diseases brought to them accidentally -- or on purpose -- by visiting ships. When millions of lives are threatened, it's a job for the Interstellar Medical Service, and a Med Ship is sent to solve the problem. Calhoun is the best the Med Service has, and hard experience has taught him that often the major obstacle to curing the sick is... the sick. And removing that king of obstacle may take very strong medicine.

This books is a compilation of four books released in the 1960's: The Mutant Weapon, Doctor to the Stars, This World is Taboo, and S.O.S. from Three Worlds.