Enterprise is en route to the New Paris colony to deliver much needed medical supplies, needed to counter a plague. It passes Murasaki 312, a quasar-like system. Since there is time, Kirk's standing orders require him to dispatch a scientific team to study the phenomenon. The expedition immediately runs into trouble, pulled of course and forced to an emergency landing on Taurus II, then beset by the hulking, homicidal natives of that planet. Can Spock's purely logical approach to leadership save the expedition and reunite its members with Enterprise?