Apprentice cargo-master Dane Thorson and the crew of the Solar Queen travel to the new planet Sargol to trade with the Salariki, a strange race of cat-men, for the fabulous Koros stones. When an Inter-Solar trading ship tries to cut in on their trading rights, they’re forced, according to Salariki custom, to fight a duel with a representative of the I-S ship in order to keep face. The Queen’s Captain Jellico wins, but the I-S ship leaves with a threat of further action.
Then, the Solar Queen takes off for Earth and en route a strange illness strikes them. They suspect the I-S are responsible, but can’t prove anything. Outlawed as a plague ship, they’re to be destroyed on sight lest they infect civilized planets. Thorson, Jellico, and the rest of their Terran crew must find a cure for the plague and escape imminent destruction.