The planet killer was a weapon machine left over from an unknown war, in a far part of the galaxy and it threatened too leave a path of destruction leading straight through earth's solar system. The Enterprise has its back against the wall and must fight the machine and by fighting activate the machines diabolical algorithms. This machine hull is pure neutrino, a substance so dense that phasers and photons have no affect and even in combination fire between two ships, the doomsday machines continues functioning.



The planet killer only survivor is Captain Matt Decker. Matt and Jim are academy buddies. Decker lost his crew after beaming them down on a planet the doomsday machine destroyed. The planet killer destroys by proximity, smashing planets into rumble and using the matter as fuel. So the machine is a weapon with unlimited power and capable of systematic destruction.



Decker looses no time in assuming command of the Enterprise and initiates an phaser and photo attack against the planet killer. Matt Decker thinks the machine is a monster, saying, "they say there is no devil, but I have seen him. Straight from the depths of hell." Decker thinks the machine is "Mobby Dick" and brings the enterprise too the brink of destruction before Spock considers Decker actions, suicidical and insane; Spock reasons that suicide is not rational and relieves Decker of the captains chair, too Jim's relief; Spock has acted valiantly; Decker escapes and navigates a shuttle into the machines nuclear furnance, in the front of the machine. Spock analyzes scans of the shuttles explosion and reports a notices, a drop in power, as Decker's shuttle explodes. Decker's sacrifice opens a strategy for Kirk to kill the machine. Jim says, "We will not question the wisdom of this man nor his sacrifice", Decker heroic act reveals a weakness in the machines design. Kirk is going to follow Decker's pattern but with more explosive power, as he sets the autodestruct on Decker's ship (anti matter and matter combination); Scotty must beam Kirk out at the last moment; Scotty with Spock assistence, works his magic and manage at the last second too beam Kirk out of the exploding ship; and the Doomsday machine ceases to function.



The Doomsday machine has become an important thread in subsequent Star Trek books, where the Doomsday machine was designed to destory the Borg. Star Trek IV, the enterprise team must travel back in time, capture a pair of humpback whales appeasing a cylinderical machine capable of disrupting earth's atmosphere and draining power from space stations. Similar too the Borg Cube the Doomsday machine proves too be a formable opponent of the enterprise: 1. It's defenses can not be compromised 2. It has unlimited energy 3. It does not operate on a moral code. The Doomsday machine has not feeling, compassion, or sense of purpose. Decker was right, the Doomsday machine is the destroyer. In contrast, Mobby Dick could be considered a sinister intelligence. Mobby Dick was the personification of evil; its albino skin indicative of a mutation or aberation of nature; its predatory behavior suggestive of a cruel beast bent on the ships destruction; and only the captains courage and insane determination can provide the drive to slay the monster.