In answer to a distress call, the Federation starship " Enterprise" arrives at the planet Scalos. Captain Kirk beams down with a landing party to a city with no evidence of life, except for an intermittent insect-like buzzing. Crewman Compton disappears before Dr. McCoy's eyes, and Kirk orders the away team back to the "Enterprise". Upon their return, the ship begins to experience strange malfunctions, and Engineering reports the sudden appearance of an unknown device attached to the ship's life support systems. Kirk and Spock attempt to disconnect the device but are prevented from doing so by an unseen force.