A huge cosmic cloud moves into the outer fringe of the galaxy, so Starfleet Command sends the Enterprise to investigate. Sensors show it as a strange combination of matter and energy that engulfs and feeds on the energy of planets. Its deliberate course change towards the populated planet of Mantilles indicates it could be intelligent. Kirk sees it as a threat to every planet in the galaxy and, if they can't communicate with it and make it stop, he will have destroy it.
Did You Know?
Some of the shots of Earth, shown to Spock on a computer screen as he is melding with the cloud intelligence, were taken from stock footage of Lassie's Rescue Rangers
(1973), a Filmation TV show simultaneous in production. The scenes that came from the Lassie show feature children running with a dog. See more
When Commodore Wesley appears on the computer monitor in Kirk's quarters, Wesley's shoulder is visible on another, separate view screen right next to him. See more
It would be best if you return to your origin, the way you came. Will you do this?
A long journey.
Will you return?