WARNING: The following contains spoilers for Star Trek: Discovery Season 3, Episode 2, "Far From Home," now streaming on CBS All Access.
In Season 2 of Star Trek: Discovery, Michael Burnham, Captain Pike and the rest of the ship's crew took on a villainous artificial intelligence known as Control. The system was originally created by Starfleet, and it was meant as a threat analysis system for the covert Section 31. However, over time, the A.I. turned on its masters and embarked on a mission to wipe out all life in the universe. While Burnham and the Discovery seemingly defeated Control, that may not be the case. In fact, it's possible the A.I. system actually survived in Lieutenant Keyla Detmer.
In the Season 2 finale of Star Trek: Discovery, Starfleet engaged in a massive space battle to defeat Control. The conflict ended when Burnham and the Discovery took the data the A.I. needed for victory into the future. The rest of Starfleet then proceeded to destroy its drone army and Control's leader itself, which had taken over Section 31's Leland, was killed. After arriving in the year 3188, she performed a scan to discover if there were any life signs in the universe. And since there were, this meant Starfleet had succeeded in changing the future and saved all life in the universe.
However, Control's survival may have been hinted at in the second episode of Season 3, "Far From Home," when the U.S.S. Discovery crash lands in the future. Lieutenant Keyla Detmer, the ship's helm officer, is injured in the crash, and she appears to be shaken up by the ordeal. Detmer is sent to sickbay, where the wound on the side of her head is healed. A medical officer clears her to resume her duties, but there still appears to be something wrong with her. She loses focus on more than one occasion and for a moment, it looks like she has no idea where she is. Her wound may be healed, but Detmer still isn't 100 percent herself.
There may be more than one possible reason for her condition, but it's entirely possible Control somehow was able to get inside of her. After all, the villainous A.I. previously uploaded itself into Discovery's Lieutenant Commander Airiam, an officer who had multiple cybernetic enhancements. Since Detmer herself has a cybernetic implant, it's possible that a small part of Control survived and uploaded itself into her.
Further proof of this possibility comes from the recently concluded Star Trek: Lower Decks. In the Season 1 finale of the animated series, Ensign Rutherford uploaded one of his own murderous programs, Badgey, into his cybernetic implant to take it inside an enemy ship. Therefore, something similar could have happened with Detmer -- only without her knowing. If this is the case, Control could start rebuilding and pose a major threat to everyone in the universe. x
Streaming on CBS All Access, Star Trek: Discovery stars Sonequa Martin-Green as Commander Michael Burnham, Doug Jones as Commander Saru, Anthony Rapp as Lt. Commander Paul Stamets, Mary Wiseman as Ensign Sylvia Tilly, Wilson Cruz as Dr. Hugh Culber, David Ajala as Cleveland "Book" Booker, Blu del Barrio as Adira, Ian Alexander as Grey, Tig Notaro as Chief Engineer Reno, Ethan Peck as Spock and Michelle Yeoh as Philippa Georgiou. New episodes of Season 3 air on Thursdays.