An illness sweeps the Enterprise, easily treatable for all except Spock, for whom it is fatal. Kirk arranges a tight rendezvous to get strobolin, the cure, in time to save Spock, but Orion pirates raid the cargo ship en route. Finding the Orions hiding within an explosive asteroid belt, Kirk means to strike a deal, unaware that all unsuccessful Orion missions end in suicide, with intent this time to take the Enterprise and crew along in an explosive finish.