Executive Producer: Gene Roddenberry
Producers: Gene L. Coon + John Meredyth Lucas
Associate Producer: Robert H. Justman
Script Consultant: D. C. Fontana

Story by: Laurence N. Wolfe
Writer: D. C. Fontana
Dir.: John Meredyth Lucas

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols
Dr. Daystrom: William Marshal
Commodore Robert Wesley: Barry Russo

Stardate 4729.4

Commodore Wesley visits Kirk on the Enterprise to explain to him: The Enterprise was chosen to work with M-5, a computer capable of making its own decisions and capable of taking over command. McCoy and Spock do not share the same opinion. While Spock admires the constructor of the computer, knowing very well Dr. Daystroms achievements in Duotronic computer technology already in the past 25 years, McCoy does not like the idea of a computer taking over in so many areas, but Kirk tells them: "They've told us it is an honor – so, let's be honored," and they go to welcome Dr. Daystrom.

Only some time on board and M-5 is in full operation. Dr. Daystrom tries to convince everybody of M-5's efficiency. Kirk feels his command cannot be replaced by a machine: "I think this thing down there is dangerous," he tells Dr. McCoy. Back on the bridge they are surprised by a control run. M-5 implicates all needed actions seconds before they can do so. A faked attack by two ships of the federation is defended. "M-5 has reacted better than any captain of a spaceship," Spock states. Kirk is impressed, but Spock says: "Something worries me: Computer have always served men well, but I do not want to serve under them. Captain, crewmen need someone they can trust, who trusts them and to whom they can rely. And that will always be that way. Always."

Captain Wesley congratulates M-5 and "captain Dunsel", an academy jargon for someone who is useless. McCoy brings Kirk a drink. Kirk confesses how useless he felt, while sitting in his chair and watching how M-5 did his job. Spock calls his captain to the bridge: A ship is approaching slowly and this time it is not an exercise for M-5. M-5 has already identified the ship as a container ship, unmanned, but attacks it and destroys it. No one, not even Dr. Daystrom is able to stop the computer. Because this should not have happened and the ship could have been manned, Kirk orders Dr. Daystrom to shut M-5 down and Lt. Uhura to inform Star Fleet command that M-5 was a mistake.

When M-5 turns up to be not possible to be shut down, they go into the machine room. Kirk gets hit by a confrontation with an unseen barrier and Spock, helping him up, suspects M-5 is not only capable of taking over, but also capable of protecting itself. Scotty suggests to cut of the main power source. As one of the co-workers tries to approach the line, M-5 send compact beams through, killing the man. They are not facing difficulties any more- they are facing a killer. Dr. Daystrom is devastated, but still tries to explain: M-5 needed a new source of energy for itself and the man got in its way. Kirk asks how long it will take until we all are in his way? In the briefing room, Spock confirms that the multi-electronic machine now controls all navigational, power and working systems of the ship, plus all communications and weapon systems. Spock suggests to remove connections between the systems and Scotty leaves to work with him on it.

As Spock mentions that M-5's reactions are not logical, McCoy asks him not to call that "fascinating." Spock agrees: It is interesting. Spock and Scott manage to switch over to manual steering in spite of Dr. Daystroms pleads not to do that. When Sulu and Chekov try to operate manual steering, there is no reaction from the ship. Spock lets Chekov and Sulu check the system and figures that M-5 has given them impulses of energy to make them think they work on a real energy line, while it had been switched it out long ago. "M-5 does not react like other computers," he says. "M-5 nearly behaves as a human," Dr. Daystrom agrees. He has developed a way to make computers work on human thinking patterns.

Now Wesley is approaching with 4 ships and they have no mean to communicate. Wesley does not know what has happened on the Enterprise. As he announces another exercise, M-5 acknowledges. The Excalibur is hit: 53 people dead. Wesley tries to make contact and wonders why Kirk does not answer, but Lt. Uhura cannot break M-5's lock on the communication system. Since all 4 ships are heavily hit, by now, Commodore Wesley has no choice but to ask Star Fleet command to destroy the Enterprise, in order to save their lives. Spock suggests Dr. Daystrom should talk to M-5 and he does. He speaks with him like with a close friend and tells him: we have killed, we have murdered. When M-5 tells him that they need to survive, he exaggerates and talks himself into trance, even attacking captain Kirk, who insists that M-5 must be stopped.

This is too close to his captain. Daystrom is brought to sick bay after a neckpinch. After Spock mentions that M-5 has – like any other being – the instinct to survive, Kirk gets the idea to speak with M-5 on that basis: What if it feels guilty for the murders, as Daystrom did? He's right. M-5 rejects to kill. Kirk shows the computer what it has done to the Excalibur – all are dead. To answer his question "what happens to someone who has killed," M-5 says: "death." Kirk confronts M-5 with the consequences and M-5 destroys itself. M-5 has not only destroyed itself- but all functions of the ship. They cannot get any communication. Quickly Kirk orders all systems to stay down. When Wesley sees no reaction from the Enterprise, he is sure that it is not a trap and calls off the attack.

In sickbay Daystrom is sedated. Spock sees parallels between his condition and that of M-5 and asks Kirk how he could have been so sure that Wesley did not think of the silence on board as a trap. He was not sure, Kirk says. Any other commander would have carried on his orders and attacked, but he knows Bob Wesley. Spock agrees with McCoy that compassion is the only thing a machine does not have- maybe it is the only thing which poses a machine above men, but he makes it clear that he always said machines are more effective than humans, not better. Spock is asked by McCoy whether he prefers to be with people or with machines, and says that he believes he already answered the question, but wonders how it would be to feed a computer with McCoy's patterns of thinking and to watch the resulting flows of illogic.

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