McCoy, Sulu, Kirk, and senior geologist D'Amato beam down to investigate a strange planet the size of the Moon but with the mass of the Earth. The planet has no magnetic field, but does have a well-developed atmosphere and plant life---despite the fact that the planet appears to be only 1000 years old. As the landing party is beaming down, a strange woman appears, says ``wait, you must not go,'' and kills the transporter operator.
The landing party discovers that more is afoot than reaches the eye when both they and the Enterprise are tossed wildly. Much to the surprise of the landing party, Helmsman Rahda, Spock, and Scott, the Enterprise is knocked 990.7 light years away from the planet. An autopsy performed on the transporter operator by Dr. Sanchez reveals that death resulted from disruption of every cell in his body. Spock does not know what to make of this, but returns to the planet at Warp 8.
The landing party splits up, and Sulu reports a magnetic spike, which then vanishes. D'Amato is sent in search of underground water by Kirk, but is killed by the woman who zapped the transporter operator when she says ``I am for you'' and then touches him. When Kirk tries to dig a grave using his phaser, he makes no progress, and discovers that the rocks of the planet are composed of diburnium osmium alloy. The burial is then accomplished by covering D'Amato with rocks.
Meanwhile, aboard the Enterprise, Engineer grade 4 John B. Watkins is killed by the woman when he checks the bypass circuit, but not before he warns Scott that a strange woman is aboard. The cause of his death is found to be cellular disruption of every cell in his body.
Back on the planet, the woman appears in front of Sulu and tries to touch him. Sulu tries to shoot her, but the phaser is ineffective. She manages to touch Sulu when he trips over a rock, but is only able to damage his shoulder before Kirk interposes himself and finds that she cannot harm him.
On the Enterprise, the woman rigs the engines to explode by fusing the emergency bypass circuit on the matter/antimatter integrator. The Enterprise begin accelerating out of control, and Spock estimates that the Enterprise will explode in 14.87 minutes, with no way to stop it.
Back on the planet, Kirk's phaser overloads itself and Kirk is forced to fling it away. The woman appears again and tries to touch Kirk, but is prevented by McCoy and Sulu. She identifies herself as Losira, commander of the station, but she does not register on McCoy's tricorder. Kirk follows the off-scale reading to an entrance, which then opens.
Scotty saves the Enterprise from exploding by reversing polarity on the magnetic probe and returning the magnetic flow to normal. The Enterprise then begins decelerating from its peak speed of warp of warp 15.2+ (although Rahda counts down warp 14.1, 14, 15.9, ...).
When the landing part enters the chamber, they find a glowing cube and a copy of Losira who is ``for'' James T. Kirk. At first he is protected by Sulu and McCoy, but two more Losiras then appear, one for McCoy and one for Sulu. Spock rescues the landing party at this juncture when he beams down and destroys the computer which was projecting the image of the woman Losira.
When a record tape is automatically played, they find out that the planet they are on is actually a space outpost built by the Calandans, who were all killed by a disease they created while building the planet. The outpost was left on automatic, with the computer attempting to fend off all explorers but the expected Calandan ship. As Kirk prepares to return to the Enterprise, he comments in response to a statement by Spock that beauty such as Losira's is transitory, that ``beauty survives.''