This final Voyager episode begins 23 years in the future. Voyager has made it back home. In the many years it took to return tho, the Vulcan Tuvoks' mind has been destroyed. He carried a disease they were too late getting home to cure.
Captain Janeway comes across aliens who have time travel technology. She realizes, there's a Warp Conduit in the Delta Quadrant that could bring Voyager home immediately - if she could go back in time and notify Voyager. There's one problem. The Conduit is deep inside Borg Space.
Janeway visits Tuvok. He's like a child. He scribbles tho, obsessed, working on math problems or movie reviews or something, he's convinced are important somehow. In the institution, Tuvok cries, asking for 'Janeway' to please, please come back to him.
Janeway decides to commandeer a federation shuttle and equip it with weapons technology 20 years ahead of the Borg, in the hopes of going back in time and using this new technology to guide Voyager to the Warp Conduit.
When she goes back in time and links up with Voyager, Janeway meets her younger self. The two captains disagree, arguing about the plan. The real-captain visits Tuvok asking him if it's true he has a brain disorder. Tuvok admits it's true, but it can't be cured by the facilities on the ship so he's kept it to himself.
The young Captain agrees to the older Captains' plan. To increase their chances of success the older Janeway plans to distract the Borg with her shuttle craft. The Borg actually capture Janeway and her shuttle. The Borg Queen personally assimilates Captain Janeway. But Janeway's expected this! the Borg Queen has assimilated a virus into herself that kills her. With the Borg Queen dead Voyager makes it thru the Warp Conduit back to federation space.