03 - This World Is Taboo by Murray Leinster

Calhoun is an Interstellar Medical Serviceman on a mission to the forbidden planet of Dara. But venturing into this taboo territory poses a deadly risk if he breaks quarantine, he’ll be seen as a plague-carrier, making him a target for anyone from Weald. Yet, what’s a story without a little risk? As tensions rise, Calhoun finds himself under fire from mysterious men of Dara. What secrets lie within this perilous world? (Summary by Mark F. Smith)