In the year 2404, the Federation and the re-assembled crew of
Voyager are celebrating the 10th anniversary of the ship's return to Earth, 23 years after it was stranded in the
Delta Quadrant.
Kathryn Janeway – now an admiral – reminisces with her crew, but reflects on the high personal costs of the long journey. She launches a plot to undo some of them by intervening at a key point in their history, changing a decision she now regrets. She steals an illegal time travel device and – with the reluctant help of now-Captain
Harry Kim – takes a shuttlecraft back to 2378, where she meets up with
Voyager, still in the Delta Quadrant. She pulls rank on younger Captain Janeway and orders the ship to return to a nebula filled with
Borg that they had passed a few days before. She provides advanced technologies that allow
Voyager to survive the massive Borg defenses, destroy two Borg vessels, and enter a transwarp corridor, which the Borg use for interstellar travel.
Voyager comes upon a Borg transwarp hub, which connects distant parts of the galaxy, and could save the ship from sixteen more years stranded in the Delta Quadrant. However, Captain Janeway wants to use Admiral Janeway's future technology to instead destroy the transwarp network; the Admiral states that this can only be done from its terminus in the Delta Quadrant, before explaining that 23 additional crew members will die on the remainder of their trip home, including
Seven of Nine (whose death will emotionally devastate
Chakotay), and that
Tuvok will develop dementia from a neurological condition that could have been treated in the Alpha Quadrant. Troubled by the choice, Captain Janeway discusses the issue with the crew, who agree that destroying the hub – severely diminishing the Borg threat to the Alpha Quadrant – is more important. The admiral is inspired by their spirit, and works with the captain on a scheme to do both. The admiral takes her shuttlecraft and enters the transwarp hub, arriving at the
Unicomplex – the center of all Borg activity and the home of the Borg Queen. She pretends to offer a deal in defiance of the captain's plans: her future technologies, in exchange for sending
Voyager safely home. However, the Queen captures the admiral and begins to assimilate her into the Borg collective. Admiral Janeway then turns the tables by unleashing a pathogen she was carrying in her bloodstream into the collective, devastating it and killing the Queen. The Unicomplex suffers a cascade failure and explodes, killing the admiral as well. Meanwhile, Captain Janeway and
Voyager have entered a transwarp corridor, pursued by a surviving Borg sphere that is trying to destroy
Voyager and crew in a last-chance attempt to create a
time-travel paradox that will undo the devastating damage that Admiral Janeway has just done. Unable to fight back against the sphere's defenses, Captain Janeway takes
Voyager inside it, destroying it from the inside just as they emerge from the collapsing transwarp corridor near Earth. They are met by a fleet of Starfleet vessels that had been sent to confront the Borg, which instead escort
Voyager home to Earth. B'Elanna Torres gives birth to her and Tom Paris’ child. ==Production==