In 2293, retired Starfleet officers James T. Kirk, Montgomery Scott, and Pavel Chekov attend the maiden voyage of the USS Enterprise-B. During the shakedown cruise, Enterprise is pressed into a rescue mission to save two El-Aurian refugee ships that have been snared by a massive energy ribbon. Enterprise is able to save some of the refugees before their ships are destroyed, though one of those saved unsuccessfully pleads to be returned to his ship. Enterprise becomes trapped by the ribbon, and Kirk goes to a control room to help the ship escape. While Enterprise is freed, Kirk is presumed dead after the trailing end of the ribbon hits the ship's hull where he was working.
In 2371, the crew of the USS Enterprise-D is in a holodeck computer simulation, celebrating the promotion of shipmate Worf to lieutenant commander. Captain Jean-Luc Picard learns his brother and nephew have been killed in a fire, and is distraught that the Picard family line will end with him. Enterprise receives a distress call from a stellar observatory where an El-Aurian, Dr. Tolian Soran, launches a probe at the nearby star. The probe causes the star to implode, creating a shockwave that destroys its planetary system. Soran kidnaps Enterprise engineer Geordi La Forge and is transported off the station by a Klingon Bird of Prey belonging to the Duras sisters, who are assisting Soran in exchange for weapons plans.
Enterprise crewman Guinan tells Picard that she and Soran were among the El-Aurians rescued in 2293. Soran is obsessed with reentering the energy ribbon to reach the "Nexus", an extra-dimensional realm that exists outside of normal space-time. Soran—who lost his family when his homeworld was destroyed—wants to escape death through the Nexus, which Guinan describes as "pure joy" and where time has no meaning. Picard and Data determine that Soran, unable to fly a ship directly into the ribbon, is altering its path by removing the gravitational effects of nearby stars. He plans to destroy another star to bring the ribbon to him on the planet Veridian III, killing millions on a nearby inhabited planet in the process.
Upon entering the Veridian system, Picard offers himself to the Duras sisters in exchange for La Forge, but insists that he be transported to Soran directly. La Forge is returned to Enterprise, but unwittingly exposes the ship's defense details. The Duras sisters attack, and Enterprise sustains critical damage before destroying the Bird of Prey. When La Forge reports that Enterprise is about to suffer a warp core breach as a result of the attack, Commander William Riker evacuates everyone to the forward saucer section of the starship, which separates from the engineering section just before the breach occurs. The resulting shockwave sends the saucer section crashing onto the surface of Veridian III, damaging it beyond repair.
Picard fails to stop Soran from launching another probe and they enter the Nexus. Picard finds himself surrounded by an idealized family, but realizes it is an illusion. He is confronted by an "echo" of Guinan left behind in the Nexus. Guinan sends him to meet Kirk, safe in the Nexus. Though Kirk is at first entranced by the opportunity to make up for past regrets, he realizes it lacks danger and excitement. Having learned that they can travel whenever and wherever they wish through the Nexus, Picard convinces Kirk to return with him to Veridian III, shortly before Soran launches the probe.
Working together, Kirk and Picard distract Soran long enough for Picard to lock the probe in place; it explodes on the launchpad and kills Soran. Kirk is fatally injured in the effort, and, after he dies, Picard buries him on the mountain. Three Federation starships arrive to retrieve Enterprise's survivors from Veridian III. Picard muses that given the ship's legacy, Enterprise will not be the last vessel to carry the name.
The starring cast of Star Trek: The Next Generation reprise their roles in Generations. Patrick Stewart plays Captain Jean-Luc Picard, Jonathan Frakes plays Commander William T. Riker, LeVar Burton plays Lieutenant Commander Geordi La Forge, Brent Spiner plays Lieutenant Commander Data, Gates McFadden plays Chief Medical Officer Commander Beverly Crusher, Michael Dorn plays Lieutenant Commander Worf, and Marina Sirtis plays ship's counselor Commander Deanna Troi. Recurring characters from the series return, including Barbara March and Gwynyth Walsh as the villainous Klingon sisters Lursa and B'Etor Duras, Patti Yasutake as Enterprise nurse Lieutenant Alyssa Ogawa, and Whoopi Goldberg as Enterprise bartender Guinan.
Malcolm McDowell plays Tolian Soran, the film's antagonist.
In the film's initial script, the entire principal cast of The Original Series was featured, but only three members appear in the film: William Shatner as Captain James T. Kirk, James Doohan as Montgomery Scott, and Walter Koenig as Pavel Chekov.
Alan Ruck plays Enterprise-B captain John Harriman.
Kim plays Enterprise-B helmsman Demora Sulu.
Glenn Morshower played an Enterprise-B navigator
Many of the minor characters throughout the film appeared in different roles in the television series. Tim Russ, who appears as an Enterprise-B bridge officer, played a terrorist in "Starship Mine" and a Klingon in "Invasive Procedures", and later joined the cast of Star Trek: Voyager as the Vulcan Tuvok. Various background roles were played by the main cast's stunt doubles
seventh film in the Star Trek film series.