t some point after the Outbreak, the sanctuary that was Terminus is disrupted when Gareth, Mary, Alex et al are terrorized by an unknown gang. Their women are raped, their people are murdered, and the survivors locked in a train car. Gareth vows to survive, emerging as the leader when his group takes back control of Terminus as a newly lethal band of cannibals.
Gareth appears in the large factory room that Carl, Rick, Daryl and Michonne go inside of after sneaking into Terminus. Gareth questions them, asking if they are there to rob them, which they respond to and then if they are there seeking sanctuary. He orders them to drop their weapons and Alex frisks them. Gareth warns the four of them not to try anything stupid and has Alex show them around Terminus. Rick, after noticing the Terminus members possessing several items belonging to members of the prison group such as Daryl's poncho, Hershel's pocket watch, the riot gear, and the orange hitchhiker's bag, Rick takes Alex and holds a gun at his head demanding to know where their people are and why their group has the pocket watch, riot gear and poncho. Gareth lies, claiming to have taken the riot gear off of a dead cop and that they found the poncho on a clothesline. After a Terminus Resident accidentally shoots and kills Alex while aiming at Rick, a shootout ensues and Rick, Carl, Daryl and Michonne flee, only to be stopped when Terminus residents line up along the outside of the fence at the back entrance with guns pointed at them. Gareth orders the four of them to lower their weapons. After this, Gareth calls them by specific code-names to walk towards the boxcar: Rick (Ringleader), Daryl (Archer), Michonne (Samurai) and Carl (Kid) in that order.
Between the events of the end of season four and the beginning of season five, it's understood that Gareth orders the dismemberment, and probable devouring, of his own weak-willed younger brother, Alex, after the latter's death by friendly fire in the season four finale.
Gareth appears as Rick, Daryl, Bob, and Glenn are gagged and leaned over a trough in a building adjacent to the train car "A". Gareth enters, interrupting one of the Terminus Guards just as he is about to knock out Glenn, asking for the "shell count" from them. After hearing muffled sounds from Bob, he reluctantly pulls down Bob's gag, after which Bob pleads that there is another way to resolve everything, and that they have plans to fix everything. Gareth laughs, telling Bob "the world can't go back", shortly before putting Bob's gag back in. Gunfire is heard after, interrupting Gareth and the Guards again. After, Carol, not seen at first, blows a hole in the gasoline tank outside, and lights it using a firecracker, to which Gareth runs outside.
Gareth is later seen as the group escapes, and is shot in the arm by Rick as he lays down cover fire for the other escaping members of his group.
Gareth is seen at the end of the episode (although it is likely he was watching the group as they camped out in the woods prior) after his group knocks Bob unconscious. As Bob awakens, Gareth says that Bob is not dead yet and says the Terminus group never intended to hurt anyone, but now his hand has been forced after the shootout and the loss of Terminus. Bob looks down to find his left leg amputated, which is now cooking over the fire for Gareth and several Terminants to feast on.
"Four Walls and a Roof"
Gareth continues talking to Bob until Bob reveals that he was bitten, allowing Gareth and his group to realize that they have eaten infected meat. Infuriated, Gareth then knocks Bob unconscious and leaves him near the church entrance for Rick's group to recover him. Later, he and his group watch Rick leave the church with a posse before approaching quietly and breaking in, taunting the remaining survivors that are sheltering in Gabriel's office. Rick and his posse, having snuck back inside, ambush Gareth by killing two of his men with a suppressed pistol, then shooting off two of his fingers, forcing him and the others to surrender. Now at Rick's mercy, Gareth begs him to let them go and tries desperately to justify his cannabilism and the cruelty Rick had witnessed. Rick, unwilling to risk letting Gareth harm others, brutally hacks him to death with a red-handled machete - as he had promised him earlier. He is later buried by Tyresse along with the other Terminus members that were murdered.