An injured member of the dangerous cybernetic race known as the Borg is discovered by the Enterprise crew and brought aboard for examination. During the following interactions, they rethink their attitude towards the Borg.
The Enterprise discovers a wrecked Borg scout ship with a single survivor: a young Borg drone. Dr. Crusher insists on treating the surviving Borg despite the past death and destruction the Borg have caused within the Federation. Captain Picard is extremely concerned, but allows Dr. Crusher to continue, provided that the Borg is confined and monitored by security forces at all times and is unable to contact the Borg Collective.
Chief Engineer La Forge and Commander Data assist Dr. Crusher in bringing the Borg back to health. As they come to understand the workings of the Borg, La Forge and Data postulate an idea of using the Borg drone as a weapon of mass destruction. By implanting an unsolvable geometric formula into his mind and returning him back to the Collective, the formula should rapidly spread (similar to a computer virus) and disable the Borg. Dr. Crusher is aghast at this suggestion, considering it equivalent to genocide, while Picard and the other senior crew deliberate on the ethics of this plan.
The Borg eventually gains consciousness. Initially calling himself "Third of Five", he ends up referring to and understanding himself as "Hugh" -- the name given to him by La Forge. Hugh discusses how the Borg only wish to learn about other cultures through assimilation, but La Forge counters this argument, discussing aspects of individuality that make them human and unique. In further debates, La Forge finds himself becoming a friend to Hugh, and begins to doubt his previous idea of genocide. This is further complicated when Hugh shows elements of individualism. The crew now debate whether it is appropriate to sacrifice one individual to protect the majority, though Picard is still insistent on destroying the Collective.
Finding Picard to be unwavering on the plan, Dr. Crusher and La Forge arrange to have Guinan (who has a similar loathing for the Borg because they destroyed her homeworld) speak to Hugh. She finds Hugh to be not a mindless drone but a young confused man, and she agrees Hugh is no longer a Borg. Guinan convinces Picard to meet with Hugh, as well, and he comes to the same conclusion, in part because Hugh refers to himself as "I" instead of the Borg's collective "we" during their discussion. Recognizing Hugh as an individual, Picard abandons the proposed plan and instead offers Hugh asylum within the Federation. Hugh expresses enthusiasm at the prospect of remaining with La Forge but ultimately refuses, recognizing that the Borg will still come looking for him. Hugh offers to be returned to the crash site, where he will be found and re-assimilated by the Borg. Picard hopes that, once Hugh is reconnected, the sense of individualism Hugh has learned will spread throughout the Collective.
La Forge accompanies Hugh to the crash site and, from a safe distance, watches the Borg recover him. Just as the Borg transport out, Hugh turns to give La Forge a parting glance.
The design of the Borg prosthetics as used in "I, Borg" was an evolution from those previously seen in the series. Michael Westmore's make-up team developed a removable eye-piece for Hugh, using magnets to allow the actor to remove it as required by the script. The team wanted the eye-piece to be dramatic, but decided against using a laser as this had been previously used for Locutus of Borg. They instead opted for a hologram and a series of LEDs that were powered by a battery pack built into the costume and mounted on the actor's back. The arm piece was also redeveloped; rather than a single "club" piece as previously used for the Borg, it was built from a foam-rubber glove with attachments.
Jonathan Del Arco had no concept of what a Borg was prior to the audition. He received his script on the evening prior to meeting with the producers and felt that it gave him a decent sense of the character. At the audition, there were another 10 to 15 actors, and they were each talking to each other and saying that they weren't sure how to undertake the role. Instead, Del Arco later explained that he was deliberately anti-social in order to get into Hugh's mindset. When he performed for the producers, someone else read the lines assigned to Picard and La Forge, and he felt like he immediately got a positive result. He received a call back, and return to audition once more. He said that his performance in "I, Borg" was driven by the memories of watching a childhood friend die, and the innocence that he felt given to his friends memory over time; "When I first read the script. I heard his voice, that's what it sounded like - full of wonderment and confusion about everything. That, to me, was Hugh." Following his appearance in the episode, he later pitched a couple of story ideas to the producers to feature the return of Hugh. He was happy when the character later returned in the sixth season finale/seventh season opener "Descent", which he felt was similar to his previous ideas.