Three former Borg drones, linked to Seven of Nine by a crash years earlier, come aboard Voyager seeking to break the bond she imposed on them.
While Voyager is visiting the Markonian Outpost, three visitors are secretly in telepathic contact with each other. They are former Borg drones, Two, Three and Four of Nine, and they try to attach Borg technology to Seven of Nine as she regenerates. Seven captures them, and the Doctor finds that they share a neural link left over from a small Borg subunit, or unimatrix, that included her.
Flashbacks reveal that years earlier, the four drones survived a crash on a planet and began to regain their individuality, but Seven, afraid of being alone, linked them back to the Collective. Now the Doctor can free them, but they will survive only about a month. Seven chooses to let them live their last days as individuals, and each of the three spends them differently, one choosing to travel with Voyager. The sixth-season episode deals with guilt and freedom, and shows how much Seven has changed.