Aidan informs Sam that the mission is coming to end-the client, Polyhedrus, has ordered Byzantium to kill Jack Turner. Realizing that the mission is the only thing keeping her alive, Sam desperately searches her hazy memory as to why Polyhedrus wants her dead, but remembers nothing. Aidan asks her to retrieve the case from Jack's study with the evidence being used as blackmail.
Outside Eddie's birthday party, Byzantium plants an explosive device on Jack's car. Just as Jack is about to step inside, he asks his grandson to join him. Sam fakes an ankle injury to pull the boy away from the car. Eddie runs over and the bomb goes off. Jack is only slightly injured, but Sam's cover is effectively blown.
Back at the house, Bingham poisons the water he's been giving to Sam. A troubled teenage girl who lives in the house across the street witnesses it from her window and sends a message to Stephen. She tells him that Tyrone and his father killed his wife, and now they're doing the same to Sam.
Sam summons her strength to look for the case, but before she can take it, Bingham walks into the study. He takes her phone and forces her to drink the poisoned water.
Following up on the girl's lead, Stephen confronts Tyrone at Dave Ryder's old bar. Tyrone isn't rattled by the encounter and doesn't deny killing Stephen's wife. Instead, he tells Stephen that he's been a better son to Jack than Stephen ever has. Stephen returns home and sends Eddie to a friend's house so he can confront his father. When pressed, Jack tells his son his bidding and blackmailing for the Khyber dam was about revenge: Polyhedrus is responsible for the death of Stephen's other brother, and Jack won't be satisfied until he kills the corporation.
Jack meets with the Pakistani minister Soomro to share the evidence he has of the mass murder Polyhedrus carried out to secure the Khyber dam. He provides Soomro with a soil sample from the briefcase the Blank-faced Man delivered in the guise of Horst Goebel. The Byzantium team analyzes the sample and finds it contains no evidence. With Jack holding zero leverage, Soomro walks out of his office, prepared to sign the dam contract over to Polyhedrus.
Jack is incensed and orders everyone out of the house except for Sam. He puts the house on lock-down so no one can get in or out and climbs the stairs to Sam's room. He holds a weakened, poisoned Sam under the water in the bathtub. Sam fades in and out of consciousness and flashes back to her childhood and the memory of a man, missing part of his finger, holding her down in the Oast houses on Hector Stokes' estate.
The Blank-faced Man, who has watched Sam's poisoning through his own security cameras, provides Aidan with a needle he says will help Sam. Aidan fights with Bingham outside the Turner house and kills him.
After Jack leaves Sam for dead in the tub, she finally lets out a breath and pulls herself out. She spots Jack leaning by the railing and knocks him over. Turner falls to his death while Sam collapses to the floor. Aidan rushes in and injects her with the needle, reviving her. "You're late," she chides him.
The Blank-faced Man meets with Keel. He has the briefcase with the real evidence against Polyhedrus, and he offers in exchange for Sam. Later, Crane gives Keel his letter of resignation, but Keel enlists him for one final mission.
Orla uses Zoe to lure Sam out onto a nearby bridge. Gun in hand, Orla approaches Sam, who seems as if she's just been betrayed. But before Orla can shoot her, Sam is taken out by a faraway shot and falls over the bridge. The sniper is Crane and he's shot her with a squib, just like in Tangier.
A healthy Sam returns to Scotland, where she picks up and plays with the child she'd never actually lost.