The scene opens with Sam narrating the book “The Snow Maiden”. The scene changes and Sam goes for her jog and remembers more of what happened to her. However, she gets sick and vomits. Aidan comes to meet her and tells her that Jack is to be eliminated. Aidan says that her time is running out and that the client won’t need her after this. He says that she is going to have to remember what she saw. She tells him that she can’t remember what she has tried to forget all these years. He tells her that she won’t have to be afraid anymore if she remembers. Meanwhile, Zoe has a blank stare on her face in bed and Andrew asks what is going on. She undresses and attempts to have sex with him, but he stops her. He says that they need to talk. He asks what is wrong and she tells him that it is a big job that she is worried about. He tells her to let him in, but she tells him that she can’t talk about work and he should know that.
Jack shows Bingham that he gave Sam something in a small dose to slow her down. He tells him that they will keep it up until Rahim signs the deal. Sam comes downstairs and is clearly not feeling well. She asks Eddie if he is excited for the party and he says that he is. She asks Stephen what is wrong when he avoids her. He tells her that things are complicated right now. Jack gets his coat and they all leave for Eddie’s birthday party. They get to the place and the Byzantium team is watching. Zoe gets the bomb and plants it while Sam, Jack and Stephen are watching Eddie go around the race track. Bingham offers Sam some champagne, clearly dosed with the chemical that Jack gave him. Jack says that it is shameless to use Eddie. He says that they will let her go when the time is right. They leave the party and they are about to detonate the bomb. However, Jack invites Eddie with him. Sam walks toward the car and pretends to have a hurt ankle. This gets Eddie away from the car and they detonate the bomb. Jack is injured, but not dead.
They get home and Jack asks about Sam’s ankle and she tells him that it is fine. Jack pretends that nothing is wrong and tells him to go open Eddie’s presents. Stephen asks Jack what happened and Stephen says that this is all about the dam and Stephen says that he is taking Eddie. Jack tells him that the safest place is in the house and tells him that Sam knew about the bomb because she saved Eddie from it. Bingham brings in the presents and asks for Sam’s phone. Aidan quickly erases the data. Aidan asks what they are going to do to get Sam out. Deacon says that the moment she saved Eddie, she knew that she was going to die. Aidan says that they need to get Sam out, but Deacon says that they have a mission and then they will get her. Aidan and Deacon begin to fight when Keel comes in. They ask how they are going to get the case out and Deacon says that there is another way. In Sam’s room, Bingham gives some drops of the liquid into her water. The girl who cuts herself and lives across the street watches him do it.
Deacon gets into their hideout and tells the team that Radim is going to Turner’s house tomorrow with Aidan to sign the deal. They need to verify the evidence and destroy it. Then they can get Sam out. Stephen comes in and tells Sam and Eddie that it is time for dinner. However, Sam tells him that she wants to lie down. She gets to her room and drinks the water that Bingham added the liquid to. Orla is watching the news when the Blank Faced Man enters. He tells her that he is there to talk. He tells her that she knows how this will end. Orla says that she doesn’t disappoint. He tells her that one of them will walk away and the other won’t. Stephen gets downstairs and the housekeeper gives him a letter. He opens it and it is a note for him to meet outside. He sees the girl who cuts herself outside and she walks off. He follows her and demands what she wants. She tells him that she saw a man kill his wife and that she is telling him now because they are doing the same thing to Sam that they did to his wife.
Inside the house, Sam is on the floor clutching her stomach. She remembers more of what happened to her as a little girl. She gets downstairs when Bingham is outside. She finds the case, but Bingham is coming inside again. Deacon calls Bingham’s phone to warn Sam. Bingham asks her what she is doing in Jack’s office and she tells him that she came for Eddie’s things. Bingham sees that the wall is not disturbed and apologizes. Stephen gets dropped off at Dave Ryder’s bar and sees Tyrone there. He is the man who killed his wife and he tells him that he knows it. Tyrone laughs and asks Stephen if he knows who he is. Stephen asks who he is. Aidan and Radim arrive at Jack’s office and are searched. Bingham takes Sam and they beat her up a bit and force her to drink more water with the liquid in it. The Blank Faced Man watches it through the smoke detector.
Jack invites Radim and Aidan into his office and tells him that he has the evidence that will destroy Polythesus. Jack is confident that the sample is legit and that he can test it himself. He gets one vile and gives it to Aidan. He walks off looking around. Bingham asks him if he is looking for someone. He is suspicious, but Stephen comes in demanding to talk to Jack. He asks the housekeeper where Sam is and he is told that she is resting. Stephen has Eddie and the housekeeper leave the house. Aidan gets into the hideout and gives the sample. Sam awakens and tries to reach for the door. She remembers more of what happened to her. The sample is taken to Keel and he gives it to Simran. She tells him that she will have the results soon. Jack meets with Stephen and he tells him that he found out that Tyrone is Jack’s son and asks why he wants the dam. He tells Stephen that it is for vengeance because it was Polythesus that stopped him from building his business and killed Stephen’s brother. Even though it was Pakistan men who killed him, Polythesus was pulling the strings. He tells Jack that he knows that Jack ordered the hit on his wife. Jack tells him that she was going to take Stephen and Eddie away and that he would have lost him.
Stephen is not happy at all of what happened and walks out. Back at Byzantium, Ian tells Keel that it has been good and thanks him for giving him a chance. The results are back and Keel calls Deacon the news. Deacon smiles and tells Aidan to get back to the house and says that it is not what they thought. Stephen tries to get Sam and Bingham tells him that she is not going anywhere. Aidan gets back with the news and tells Radim. He says that they are done and says that the evidence was plain fertilizer. He tells Jack that he has been had and so has he. Jack gets a crazy look in his eyes. Stephen calls the police and Jack tells Bingham to get everyone out except Sam. Aidan says that he is going back in. Jack is inside and sets the house to be on lockdown. The Blank Faced Man tells Aidan that he needs to get in the house and give Sam medicine. He doesn’t trust him, but the man says that he doesn’t need to kill someone who is already dying. Jack enters Sam’s room and runs the bath.
Outside, Aidan asks Stephen how he gets in. Bingham has the override key. Bingham holds Aidan at gun point and Aidan fights him. Inside, Jack is drowning Sam and she remembers how the man who hurt her had five fingers. Aidan manages to get the upper hand and stabs Bingham. Sam is inside unresponsive. Jack walks away and leans over the railing. Aidan manages to get the keys off Bingham and Sam comes to again. She gets out of the bath and pushes Jack over the ledge. He falls to his death. Aidan enters and gives Sam the medicine. At a café, the Blank Faced Man sits with Keel and tells him that he has the samples of the sediment. He tells Keel that he wants someone in return.
Sam takes down her wall of conspiracy. She sees an article of Hector and there is a hand with a finger missing touching his shoulder. Sam has to find the man with the finger missing. Aidan packs Sam up and asks her when she will be back. She tells him that she needs answers now. He says goodbye to her and she hugs him. She looks at the key with answers to Aidan’s identity in her hand. Zoe gets home to find Orla there. She tells her that she needs Zoe to give her Sam. Deacon comes into Keel’s office with his letter of resignation. He tells him that he is done. However, Keel tells him that the Blank Faced Man has the evidence and that he will expose Polyhedrus unless they deliver Sam to him. He says that he is competing to take her life. He asks Deacon what he would do and Keel tells him that they are going to finish this once and for all, but he needs Deacon’s help in this.
Sam says goodbye to Eddie and Stephen. He tells her that he finished her mother’s book. She asks if he found the ending sad and he asks if the snow maiden really died. She hugs him and they leave. Zoe calls Sam and tells her that they need to meet on the bridge. She tells her that she is on her way. Zoe waits for Sam to arrive. Sam comes up to her and sees Orla coming at her as well as two men on the other side of the bridge. Zoe asks her what is going on and suddenly Sam is shot by Deacon with a sniper rifle. She falls over the edge. One moth later, we see Sam climbing to the top of the hill to her family home. A car pulls up and Sam retrieves a baby from it. She hugs her baby and narrates the ending of the Snow Maiden. The season ends.