Trama

The USS Enterprise encounters the wrecked USS Constellation and its distraught commodore who's determined to stop the giant planet-destroying robot ship that killed his crew.

The U.S.S. Constellation and its crew were destroyed by a giant robot ship which consumes planets for fuel, leaving only a guilt-ridden Commodore Decker aboard the crippled ship. Kirk beams over to begin repairs while Decker beams aboard the Enterprise. After Kirk loses radio contact with the Enterprise, the obsessed Commodore seizes command of the starship, determined to destroy the planet-killer, even at the cost of Kirk's ship and the entire crew.—fkelleghan@aol.com

While on patrol, the Enterprise approaches a recently mapped solar system only to find that all but two of its planets have been destroyed. They also find another starship, the USS Constellation, floating in space and apparently abandoned. Beaming aboard the Constellation, they find only one occupant, Kirk's friend and the ship's commander, Commodore Matt Decker, who tells them of his encounter with a huge planet-killing machine. With Kirk attempting to re-start the Constellation's engines, Decker takes command of the Enterprise and, in his irrational state, announces he is going to try and destroy the doomsday machine.—garykmcd

Commodore Decker (William Windom) is a madman. While his star-ship, the Constellation, was being attacked by a huge alien killing device, he beamed his people to safety on the surface of a planet, and then the device destroyed the entire planet, leaving the Commodore alone on the ship. Imagine seeing all of your crew killed and you are the only survivor.

This is how Kirk and the Enterprise find Decker, insane and alone in the Captain's chair on the Constellation. They beam him back to the Enterprise and Kirk and a small landing party, including Scotty, remain on the Constellation in order to repair it. The Enterprise could have simply escaped, but this giant planet-killer (which looks like a large horn) is on a direct path to Federation space, so somehow, Kirk must destroy it. By studying the tapes of the Constellation, Spock determines that the attacking ship is a robot that was designed by an ancient civilization (from a different galaxy) at the time of war to hunt and destroy enemy planets. By destroying the planets, it generates materials and energy to feed itself. The war has perhaps ended and the civilization faded, yet the robot lives on, killing planets and star systems to sustain itself. It is on a direct course through the most populated areas of the current galaxy.

The Commodore, on board the Enterprise now, regains his composure. He tells Spock they must destroy this thing, as it attacks the Enterprise. Lt Palmer (Elizabeth Rogers), the lovely blond communications officer (Uhura is not on duty) loses communication with Captain Kirk on the Constellation, and Decker seizes his chance, and takes control of the Enterprise under the Federation guidelines which state that the ranking officer may assume command.

He throws all the power of the Enterprise at the planet killer, he drains the ship's power in a fruitless cause, and now both ships are helpless. Kirk finally makes contact with the Enterprise and tells Spock, orders him, to assume command. Decker finally gives up, but secretly steals a shuttle-craft and tries to explode the planet-killer from the INSIDE. The shuttle is too small, and it is a suicide mission. Decker is destroyed in his insane mission. Kirk and Spock note a minute drop in the device's power after the shuttle-craft hit it. Kirk surmises that the shuttle-craft explosion damaged it, slightly.

Meanwhile, Kirk thinks Decker was right, but he wants to use the Warp Core of the constellation, which is a more powerful explosive. Spock and Lt Palmer get Kirk's message to beam Scotty over after the bomb has been set. Scotty says good luck. Kirk must stay on the Constellation in order to turn the detonation switch, after which he will have 10 seconds to beam back. Spock gives the all-clear, Kirk flicks the switch, but the transportation pad on the Enterpise has a short-circuit. Scotty rushes to fix it. Kirk says impatiently "Gentlemen, beam me aboard." Just as the Constellation explodes inside the planet killer and destroys it, the transporter engages, but we don't know if Kirk's molecules survived the explosion. It takes a few moments, but finally, Kirk is aboard.