Lester del Rey - Badge of Infamy (version 2)

Set in the early 22nd century: Dr. Daniel Feldman, stripped of rank and status and named pariah for violating Medical Lobby rules, stows away on a spaceship and flees to Mars Colony. There, while essentially practicing medicine without a license, he stumbles upon a plague organism indigenous to Mars, that threatens the whole colony and potentially the human race. Performing research to identify a cure, (also in gross violation of Medical Lobby rules) he must risk his life to buck the entrenched bureaucracy, bent on sweeping the whole matter under the rug in the name of political expediency. — Summary by Thomas Rose