Star Trek: Voyager Season 6 Episode 26

Stardate: Unknown. Seven of Nine is led to a place known as Unimatrix Zero; a place where Borg drones are individuals for a short period of time during their regeneration. However, once their regeneration is complete, all recollection of the event is erased. Captain Janeway uses this to form a plan of attack that would create a mutiny from within the Collective.