Spock falls gravely ill, and when Orion pirates steal his cure from a Starfleet freighter, the Enterprise must hunt them down in time to save him.
On the way to Deneb V, Spock contracts choriocytosis, a disease that is deadly to Vulcans, and McCoy can only slow it. The Starfleet freighter Huron is due to deliver the cure, but Orion pirates attack it and carry off its cargo of dilithium along with the medicine.
The Enterprise finds the battered Huron and pursues the Orion ship. Kirk meets the Orion captain on an unstable asteroid and discovers he is carrying explosives rather than face capture. Kirk prevents the blast, recovers the medicine and saves Spock, and the captain is held for trial. Howard Weinstein sold the script at nineteen, his first professional sale.