In a flashback, Gareth and his crew huddle in a Terminus train car while marauders torture members of their group outside. Alex laments posting "Sanctuary" signs, saying they left themselves vulnerable. "We were trying to do something good," Gareth reflects.
In the present, Rick and his group are imprisoned in the train car. They quietly build weapons using scraps stripped from their clothes and the car's interior. Their captors release tear gas into the car, catching them off guard.
Rick, Daryl, Glenn and Bob are brought to a human slaughterhouse, where Terminus residents begin bludgeoning and slitting other captives' throats. The first to be slaughtered is Sam – the young man Rick and Carol met on a supply run before Carol's exile.
Gareth interrupts to interrogate Rick about the bag he stashed in the woods. Rick admits it's filled with weapons, including rifles, handguns, a compound bow and a machete. Of the latter, he tells Gareth, "That's what I'm gonna use to kill you."
Gunshots suddenly resound outside, followed by a massive explosion.
Earlier that day: Carol, Tyreese and Judith make their way toward Terminus. They hear gunfire erupt and watch a herd of walkers flock toward the noise.
They happen upon a cabin where Martin, a Terminus resident, is setting up fireworks to deter walkers away from Terminus. Carol and Tyreese hear him mention "the chick with the sword" on a walkie-talkie and hold him at gunpoint.
Carol takes Martin's explosives and sets off toward Terminus, slathering herself in walker blood to disguise herself. Tyreese, meanwhile, guards Martin in the cabin. Martin tries to convince Tyreese to take his car and leave with Judith.
At the perimeter fence, Carol sees Gareth's men drag Rick, Daryl, Glenn and Bob to the slaughterhouse. She fires at a propane tank within Terminus, then launches one of Martin's fireworks toward the breach, setting off a massive explosion. Walkers begin to swarm.
In the slaughterhouse, Rick quietly cuts his bonds with a homemade wooden shiv that he hid in his sock. He frees himself and fatally stabs his captors.
Mary sees walkers flooding through a hole in the fence and runs inside. Carol, disguised as a walker, infiltrates Terminus with the herd.
Maggie, Carl, Michonne, Sasha and Abraham's crew anxiously wait in the train car as they hear the commotion outside. Chaos reigns as walkers feast on Terminus residents. Carol takes advantage of the confusion and shoots down Terminus snipers.
Rick frees Daryl, Glenn and Bob. As they leave the slaughterhouse, they see human body parts suspended from meat hooks.
En route to rescuing the other survivors, Glenn insists on opening another train car to free the captives inside. But when they do, a deranged man runs out screaming wildly before a walker thrashes him.
Carol discovers a room filled with items pilfered from Terminus victims. She retrieves Rick's watch – which he had given Sam -- and Daryl's crossbow.
Rick's group ambushes a team of Terminus residents and takes their weapons.
Carol discovers the Terminus shrine. Mary confronts her and they struggle. As Carol gains the upper hand, Mary explains that Terminus used to be a real sanctuary until a group of maurauders raped and killed her people. The lesson, Mary explains, is "You're the butcher or you're the cattle." Carol shoots her in the leg and leaves her to be devoured by walkers.
Back at the cabin, Tyreese becomes distracted by approaching walkers. Martin gets a hold of Judith and threatens to kill her unless Tyreese steps outside. Tyreese complies, and Martin listens to his shouts as the walkers attack. Martin then goes to check if Tyreese is still alive; Tyreese bursts through the door and pummels Martin. Outside, the ground is littered with walkers Tyreese killed hand-to-hand.
Back in the train car, Eugene reveals that before the fall, he helped engineer weaponized diseases to fight other weaponized diseases. He says his team devised a system that could kill all humans on the planet — and that same system might be able to kill off the walkers.
Rick's crew rescues the rest of the group from the train car. Newly reunited, they fight their way out of Terminus.
Rick leads the group to the weapons cache in the woods. He insists they go back to kill the remaining Terminus residents, but the others disagree. "The fences are down," Maggie reasons. "They'll run or die." Carol appears. Daryl hugs her. "Did you do that?" Rick asks, embracing her as well and thanking her for saving them.
Carol leads everyone to the cabin, where Tyreese awaits with Judith. Rick and Carl run over and joyfully reunite with the baby, while Sasha embraces her brother.
As the group rests, Tyreese tells Carol that he killed Martin. Rick decides that they will get as far away from Terminus as possible. The group follows the railroad tracks until they happen upon a Terminus sign. Rick crosses out most of the text and modifies it to read, "No sanctuary."
In a flashback, one of the marauders – the same deranged man released during the Terminus firefight – enters the train car imprisoning the Terminus residents and drags a woman away. Gareth comforts Mary and vows to take back what's theirs. "You're either the butcher or the cattle," he declares.
Months after Rick's escape from Terminus, a masked stranger marches down the railroad tracks. He stops to see the Terminus sign Rick modified, and hangs his head. He removes his mask. It's Morgan.