The Immunity Syndrome

Heading for a much-needed rest, the Enterprise is diverted when contact is lost with the Gamma 7A system and with the starship Intrepid, crewed entirely by Vulcans. Spock suddenly feels the four hundred Vulcans die. Kirk finds the Gamma 7A system lifeless and a dark zone ahead that weakens the crew and drains the ship's power. At its heart is a single-celled organism thousands of kilometres long, feeding on energy and preparing to reproduce. Someone must take a shuttlecraft inside it, and both Spock and McCoy volunteer, their rivalry turning into something closer to mutual respect. Kirk sends Spock, who learns how the creature might be killed before his signal breaks up. Realising the ship must act like an antibody, Kirk takes the Enterprise inside and fires an antimatter charge into the nucleus. With Spock's shuttle held in a tractor beam, the drained ship coasts clear as the organism dies.