Plot summary
A small team from Voyager, including Seven of Nine and the Doctor, are performing a survey of a proto-nebula. When the nebula becomes unstable, the team is transported to the ship, but a malfunction briefly merges their patterns together. The Doctor finds his mobile emitter is failing, and he is returned to sickbay while Lt. B'Elanna Torres takes the emitter to the science lab for repair. The crew is unaware that the emitter has gained some of Seven's Borg nanoprobes from the malfunctioning transporter, and it begins assimilating the equipment in the science lab.
The crew soon detects a large power draw from the lab, and discover that the nanoprobes have constructed a Borg maturation chamber, rapidly growing a Borg drone. They determine that the components of the drone are based on the advanced 29th-century technology of the emitter; should the Borg of this century gain that technology, the entire galaxy is doomed. Captain Janeway decides to allow the drone to mature, hoping to make it understand humanity's individualism once it is born.
The drone (J. Paul Boehmer) soon leaves the maturation chamber, and though it immediately attempts to seek out the Borg collective, Seven tries to convince him that he is an individual. Several of the crew help the drone to integrate, purposely omitting information about the Borg collective, and soon the drone appears adapted to being an individual, requesting to be named "One".
Through the action of his nanoprobes, One involuntarily sends a signal to the Borg collective, and a Borg ship closes in on Voyager. Seven gives One a crash course on the Borg collective, and though One is fascinated by it, Seven asserts that she considers the Voyager crew her collective. One helps the crew enhance their shields and weapons, but the battle is still a losing one. One transports to the Borg ship and overrides the controls, sending the ship into the proto-nebula where it is destroyed.
The crew detects a life sign, and finds One is still alive but in critical condition. He is rushed to sickbay, but refuses treatment, explaining that now that the Borg know of him they will pursue Voyager endlessly to assimilate him. He assures the emotional Seven that she will adapt once he passes away.
Credits
Adapted from Wikipedia contributors, Drone (Star Trek: Voyager). Paragraphs and formatting adjusted; illustrations, reference markers, block quotations and non-story material omitted.