breaking free of the zone, but the effort succeeds only in bringing the ship to a halt. Their quarry is finally revealed to be a gigantic, multicolored object resembling an amoeba. Kirk launches a sensor probe into it, which reveals that the object is indeed made of protoplasm, and is alive. McCoy believes that a crewed probe must be sent into the creature to gather the data needed to destroy it, and volunteers himself for the job. Spock insists that he is better qualified. Kirk is reluctant to send either of them arguing that it would be a suicide mission and that if anyone should go it should be him as the captain. But Spock points out that Kirk is not a science specialist and is much better served commanding the Enterprise. Kirk is then forced to choose which of his two friends to send out in the shuttle, with a realistic probability they won't return. Kirk ultimately chooses Spock, agreeing that he is better equipped to handle the mission. Spock pilots a shuttle through the creature's outer membrane and makes his way toward the nucleus. Eventually, he reports that the creature is ready to reproduce, and suggests a method of destroying it, but the key part of the message is garbled. Kirk and McCoy meet to discuss the situation, and Kirk speculates that if the organism is like an invading virus, then an equivalent of "antibodies" is needed to destroy it. Kirk takes the Enterprise into the creature's body, and orders Chief Engineer Scott to prepare an antimatter bomb with a timer set for a seven-minute delay. The bomb is fired into the cell's nucleus and the Enterprise backs out using what little power remains. With seconds remaining, Spock's shuttle is finally located and Kirk orders Scott to tow it with a tractor beam. With power levels nearly exhausted, the ship approaches the outer membrane just as the bomb explodes. Both the Enterprise and the shuttle are thrown clear of the organism as it is destroyed. The Enterprise is restored to full power and sustains only minor damage. Music Music from the episode "The Doomsday Machine" was reused in this episode. Production and reception When this episode was filmed, George Takei was filming The Green Berets and therefore unavailable to portray his character, Lt. Sulu. John Winston's character, Lt. Kyle, occupied Sulu's helmsman's seat, wearing a gold command tunic