Marlene is the leader of the Fireflies, the militia fighting the military in the quarantine zones. Wounded in Boston, she hires Joel and Tess to smuggle Ellie out of the city in The Quarantine Zone, and you meet her again at the Fireflies' hospital in Salt Lake City near the end of the game.
The Quarantine ZoneThe Quarantine Zone starts the story proper 20 years after the outbreak, inside Boston's military-run zone in August 2033. As Joel, now a smuggler, you and his partner Tess slip outside the wall to track down Robert, a dealer who owes them guns, and end up taking a new job from the Fireflies.Marlene is a committed revolutionary who has watched the Fireflies thin out under the military crackdown. She is calm under pressure and pragmatic about the cost of her cause. Her bond with Ellie comes from her promise to Anna rather than from any time spent raising her.
Marlene originally hired Robert to move Ellie out of Boston and bought guns from him. After the military wipes out her squad, she finds Joel and Tess standing over Robert's body and offers them double the guns he owed them if they deliver her cargo to Fireflies waiting at the Capitol Building. Ellie wants to stay with her; Marlene tells her this is her only chance to get out.
In the hospital you can find recordings Marlene made addressed to Anna. In them she wrestles with what the doctors have asked of her, admits how exhausted she is, and accepts that Ellie will not survive what comes next.
Marlene approves the surgery that would extract the infection from Ellie's brain, knowing it will kill her. She thanks Joel, explains the plan and tells the guard Ethan to escort him out and shoot him only if he tries to stop it. When Joel fights his way to Ellie, Marlene corners him in the parking garage and begs him to hand Ellie over. He shoots her, then kills her as she pleads for her life so she cannot come after them.
Ethan
Ethan is a Firefly soldier at Saint Mary's Hospital in Salt Lake City. In The Firefly Lab he finds Joel and Ellie after they arrive, and Marlene later puts him in charge of walking Joel out of the building.
Jerry Anderson
Jerry Anderson is the lead doctor of the Fireflies at St. Mary's Hospital in Salt Lake City, the man in charge of their research into a cure. You only meet him near the end of the game, in the chapter The Firefly Lab, and his part in the story is best discovered by playing it.
Kari
Kari is a Firefly surgical assistant at Saint Mary's Hospital in Salt Lake City. You meet her in the operating room at the end of The Firefly Lab, where she is helping the surgeon Jerry Anderson.
Ellie Williams
Ellie Williams is the 14-year-old girl Joel is hired to smuggle out of Boston, and your companion for most of The Last of Us Part I. She was bitten weeks earlier and never turned, so the Fireflies believe her immunity could lead to a vaccine. You play as her in the winter chapter and in the Left Behind DLC.