In 2273, a Starfleet monitoring station, Epsilon Nine, detects an alien force, hidden in a massive cloud of energy, moving through space towards Earth. The cloud destroys three of the Klingon Empire's new K'I'Inga-class warships and the monitoring station on route. On Earth, the star ship Enterprise is undergoing a major refit; her former commanding officer, James T. Kirk (William Shatner), has been promoted to Admiral and works in San Francisco as Chief of Starfleet Operations. Starfleet dispatches Enterprise to investigate the cloud entity as the ship is the only one in intercept range, requiring her new systems to be tested in transit.Kirk takes command of the ship citing his experience, angering Captain Willard Decker (Stephen Collins), who had been overseeing the refit as its new commanding officer. Testing of Enterprise's new systems goes poorly; two officers, including the science officer, are killed by a malfunctioning transporter, and improperly calibrated engines almost destroy the ship. Kirk's unfamiliarity with the new systems of the Enterprise increases the tension between him and first officer Decker. Commander Spock (Leonard Nimoy) arrives as a replacement science officer, explaining that while on his home world undergoing a ritual to purge all emotion, he felt a consciousness that he believes emanates from the cloud. Other officers are Leonard McCoy (DeForest Kelley), the chief medical officer. Montgomery Scott (James Doohan), the Enterprise's chief engineer. Pavel Chekov (Walter Koenig), the Enterprise's weapons officer. Uhura (Nichelle Nichols), the communications officer. Hikaru Sulu (George Takei), the Enterprise's helmsmanEnterprise intercepts the energy cloud and is attacked by an alien vessel within. But this time, Spock is able to discern that the alien vessel has been trying to communicate with the Enterprise. Spock fixes the Linguacode and transmission frequencies of their reception and the attacks on the Enterprise stop. A probe appears on the bridge, attacks Spock and abducts the navigator, Ilia (Persis Khambatta). She is replaced by a robotic replica, another probe sent by "V'Ger" to study the crew. Decker is distraught over the loss of Ilia, with whom he had a romantic history. He becomes troubled as he attempts to extract information from the doppelganger, which has Ilia's memories and feelings buried within. Spock takes a spacewalk to the alien vessel's interior and attempts a telepathic mind meld with it. In doing so, he learns that the vessel is V'Ger itself, a living machine.Shortly thereafter V'Ger transmit a signal in simple binary code on radio and asks for the creator. When it receives no response, it fires probes into the atmosphere that Enterprise calculates will rid the planet of mankind. Ilia the robot tells Kirk that V'Ger has calculated that the Carbon lifeforms infest the creator's planet as it infests the Enterprise and hence needs to be eliminated to stop interfering with the creator's work. Spock suggests that V'Ger is a child and asks Kirk to treat it as such. Kirk tells Ilia the robot why the creator has not responded but won't reveal that to V'Ger. V'Ger has a huge power surge (in the manner of throwing a tantrum). Kirk holds and says to Ilia robot that he will only reveal the information to V'Ger directly. As such, the Enterprise is pulled towards the V'Ger's central brain complex.At the center of the massive ship, V'Ger is revealed to be Voyager 6, a 20th-century Earth space probe believed lost. The damaged probe was found by an alien race of living machines that interpreted its programming as instructions to learn all that can be learned and return that information to its creator. The machines upgraded the probe to fulfill its mission, and on its journey the probe gathered so much knowledge that it achieved consciousness. Spock realizes that V'Ger lacks the ability to give itself a focus other than its original mission; having learned what it could on its journey home, it finds its existence empty and without purpose. Before transmitting all its information, V'Ger insists that the Creator come in person to finish the sequence. Realizing that the machine wants to merge with its creator, Decker offers himself to V'Ger; he merges with the Ilia probe and V'Ger, creating a new form of life that disappears into another dimension. With Earth saved, Kirk directs Enterprise out to space for future missions.