Starfleet's USS Voyager, stranded on the other side of the Galaxy, once again encounters a race of cybernetic organisms called the Borg as the ship journeys back to Earth.
Seven of Nine journeys with Captain Janeway, thanks to a double mind-meld performed by Tuvok, to Unimatrix Zero and reverts to Annika Hansen, her human identity before assimilation.
Her forgotten lover Axum made contact with her so she may help them; the inhabitants of Unimatrix Zero have developed a masking nanovirus to inoculate them from detection by the Queen, but it can only be administered from the corporeal world.
Janeway refuses and plans to infiltrate a Borg ship on her own and release a version of the nanovirus, now modified to allow the Unimatrix Zero drones to retain their memories and stage a resistance.
After being blackmailed by Chakotay (he threatens to have the Doctor remove her from command if she insists on going alone), she, Tuvok and B'Elanna penetrate the Borg cube to reach the central plexus and administer the nanovirus but are caught.
Independent Borg who now, like the Queen, have the advantage of being self-aware, take command of some vessels, rebel, and start a civil war with the Collective.
[4] Ian Grey at RogerEbert.com noted this episode in their feature on Star Trek: Voyager, commenting that "Unimatrix Zero" offered a "revolution fought in the safety of dreams.
[6] Nerdist suggested watching "Unimatrix" as part of an abbreviated binge-watching guide featuring USS Voyager's confrontations with the Borg.
[7] SyFy Wire ranked "Unimatrix Zero" as one of the seven essential episodes about Borg to watch as background for Star Trek: Picard.