Last time on Person of Interest, Agent Carter returns for a flashback episode. Reese uses his memory of her to help him get through this new case and stay alive. He also learns that he regrets not letting her in on his personal life and feelings.
We're brought back to the gang war between Elias and Dominick. We see a woman driving and discovering that her breaks aren't working. She crashes and a vehicle shows up and kidnaps her. We hear a woman's voice and see that it's Control/Diane. They place another woman's body in the car along with a bomb and leave just as it detonates.
Fusco scolds Reese for not letting him in on his last case. Reese apologizes and commends Fusco on his friendship, leading Fusco to believe that he is sick. They are at a crime scene with four Brotherhood soldiers. Reese asks Finch why the machine didn't warn them. Finch is afraid that Samaritan found their machine, but Root shows up and reassures Finch that if that were the case, then they'll be dead.
A payphone rings at the crime scene and they're given the numbers for both Dominick and Elias. Reese finds agents sacking a canister for evidence. Finch gives Reese the location to where he traced two Brotherhood transport trucks.
They watch Dominic argue with one of his men. They're preparing for a fight with Elias. The canister found at the crime scene belongs to a bank that was recently bought by Elias to keep his movements secret.
Just then, Shaw's phone rings and Root answers. On the other end, Shaw asks for help but the line was cut.
The woman kidnapped from earlier, Shelly, is being questioned by Diane about Samaritan. She kills one of her agents, Tyler, in front of her, who admitted to her that he was a Samaritan mole assigned by Shelly. She threatens Shelly in order to get answers.
Root and Finch argue about whether Shaw is really alive or not. Root gets ready to find Shaw, but Finch believes the call was a trap. Root leaves anyway and Finch goes with her. They go to the roof of a building where Root threatens her own life in order to get answers from the machine. It works and the machine grants access. They head to the Steiner Psychiatric Institute where the call was made from. They go along with the machine to try and get into the heavily guarded asylum.
Reese and Fusco head to the bank that Elias recently purchased. Finch tells Reese that they may have found Shaw, but as Reese gets ready to leave, Elias shows up. Guns are drawn as they threaten to arrest Elias, but Dominick and the Brotherhood show up and corner them.
Finch and Root dig their way into a tunnel that contains feeds from the asylum, but Samaritan has caught on to Finch's laptop while he tried to hack into the server. They leave and their machine warns Root that it's too dangerous with Finch agreeing, but Root explains that both Shaw and the machine need their help now.
Reese, Finch and Elias are tied up. Dominick doesn't kill Elias because he needs access to his intel. One of Dominick's boys pulls him to the side to question whether Reese and the others will tell the truth, that when Dominick brings out the shady Harper Rose who explains to Reese and Fusco that she got an offer she couldn't refuse.
Root disguised herself as a doctor and Finch as a psychiatric patient with schizophrenia. Finch goes along with the ploy, looking for information from other patients to find Lenny. After finding him, he tells them that the doctors stole his spaceman and Lenny attacks them, distracting the guards while he hacks the camera feeds. He leads Root to the 9th floor which is heavily guarded. He leads her to room 914 where she follows someone into. She sees Greer and finds that it's Samaritans base of operations.
Diane continues to interrogate Shelly. Diane explains to her that some "friends," Reese and Finch, have convinced her to look deeper into Samaritan. Shelly begs to go home to be with her children but Diane doesn't fall for it. She shows Shelly some pictures of her with Tyler. Shelly continues her ploy but breaks after Diane shows her a picture of Shelly in the White House in which Shelly replies "You have no idea what's coming for you, b**ch."
Dominick talks to Elias about Finch, finding out Harper gave it away. Elias refuses to talk about it despite Dominick bringing up Anthony's death. He unties him and one of his men starts hitting him with a hammer, starting at his hand, working his way up.
With Elias' screams in the background, Dominick asks Reese about Finch's whereabouts and when he doesn't give answers, one of his men stabs him in his previous bullet wound with a screwdriver. Another one of his men hold's Fusco's head under a sink of water, asking him the same questions. Fusco appears to be ready to crack, but instead asks for a loofah so they can wash his back too.
A woman on Doninick's crew reveals that they have someone on the inside who has been revealing information to Elias. Harper is prepared to save Fusco when Dominick tells his man to stop. She tells Fusco that Thornhill who offered her money is she saves Fusco. They handcuff him and leave.
Root makes her way through the floor where she finds a room that had some of Shaw's belongings. Martine Rousseau, a Samaritan operative, shows up and they get into a fight, but two more Samaritan operatives show up and Martine injects root, telling her that Shaw broke and told them everything Root would do.
Reese and Elias talk about his new calm persona. Reese knows that Elias left the canister on purpose, knowing Dominick would show up. Dominick has Elias write an address on a piece of paper, headquarters for the Brotherhood. Dominick plans to have Elias' men show up with the Brotherhood expecting them, or he can reveal who his mole is.
Greer shows up and tells Root that Shaw revealed that she speaks to the machine through her cochlear implant. Greer's men bring in Finch as they prepare to take the device out of Root's head.
Martine threatens to kill Finch, telling Root that he doesn't look like a fighter and will die without so much as a peep. She gets ready to operate when Root grabs her and snaps her neck, killing her, then surrenders.
Diane continues to question Shelly. She finds out that Samaritan is planning an attack on May 6. Shelly tells Diane that this is her last chance to look away while Samaritan takes control.
Elias agrees to reveal who his informant is and gives him the account number where he has been sending money to. Dominick finds out that the name on the account was Link's, his right hand man. Elias laughs and reveals that he planned everything, and that Link was not his informant, there was no informant. Dominick gets ready to kill Elias but stops himself because he needs information. Elias remembers that Dominick blamed him for the death of his friend Anthony, so Elias asks how he feels about being responsible for the death of his friend, Link.
Greer tells Finch that Samaritan is offering their machine an ultimatum, give up its location or watch everyone die. Root ties to tell the machine not to give in and the power goes out. The machine agrees to give it's location, telling Root that it doesn't want to fail her again. The power comes back on and Greer and his men leave. Root and Finch leave.
Shelly tells Diane that Samaritan is in the process of building a better world and creating a new start for some while killing others. Diane shoots and kills Shelly.
Root and Finch try to locate the machine before Greer and his men get there and destroy it.
Next Week: The season finale of Person of Interest will bring about a war between two machines and the people trying to save them both.
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