Demolition site. Workers prepare a building to be demolished. After the final sweep, DENNIS, one of the workers, gets a strange feeling and heads back inside. Looking at the building's blueprints, which reveals a room they didn't check. Dennis finds a hollow spot in the floor and kicks it in -- revealing a dungeon of hidden passages below. A few workers follow him into the dark and eerie passages. They find a room cordoned off by bars, and inside, huddled in the corner, is a young boy: hairless, emaciated, trembling, and naked.
At the FBI, Charlie talks on the phone and receives some startling information. At the fax machine he finds a creepy invitation to an art exhibition. Charlie's look suggests this isn't just any ordinary fax.
At Olivia's apartment, Rachel and Olivia help Ella pick out an outfit for school. Rachel admits that she and Ella went apartment hunting the day before, despite Olivia's insistence that having them stay with her is no problem. Then Olivia receives a call from Charlie, who informs her that "the Artist" has returned. And just as Olivia is about to rush to join the investigation, Broyles calls and tells her to fetch the Bishops and meet him at...
Boston Children's Hospital. Broyles shows Olivia, Peter, and Walter the boy from the demolition site. The tunnel in which the boy was found had been sealed shut for at least 70 years, but somehow the boy managed to get down there -- and survive. He hasn't spoken a single word since he was found. Walter tells Broyles that he'll need a piece of special equipment: a record player. The boy's attending physician, DR. WINICK, tells the team that the boy is having trouble breathing. Walter explains that he was trapped in an oxygen-deprived atmosphere for so long that his body became accustomed to it. To get the boy breathing normally, they need to deprive him of oxygen.
A Laundromat. A man folding his clothes at a table strikes up a conversation with a female customer, commenting on her griffin tattoo. She gives him the cold shoulder. Moments later, she sees to her embarrassment that the man is wheelchair-bound. Later, the man is loading his laundry into his van outside as the woman exits. She offers help and he accepts. As she sets his basket of clothes inside the van, the man stands up behind her and pulls out a needle...
Inside the van, the man, now splattered with blood, turns on a small saw and gets to work.
Back at the hospital, Walter is proven right as the boy's breathing returns to normal. Walter instructs the doctors to increase the oxygen concentration by every hour until he acclimates to the normal atmosphere. Winick says the boy is actually in surprisingly good health; he responds to sound, he has no brain damage, and his heart and blood pressure are strong.
Olivia is trying unsuccessfully to communicate with the boy when her phone rings. It's Charlie with more details about "the Artist" case. The boy eyes Olivia as she writes down an address. And then the boy gently takes Olivia's hand and pulls her notepad into his lap. As the two lock eyes, the boy's hand writes down the words: "Sam Gilmore" upside-down.
Charlie and Olivia arrive at a crime scene. The woman from the Laundromat is dead, propped up, wearing a wig, and dressed in a gown. The officer in charge tells them that the victim's name is Samantha Gilmore.
At the FBI, Charlie briefs a room full of agents on the Artist. His M.O. is to kill women and then "enhance" their appearance to fit conventional norms of beauty; in Samantha Gilmore's case, he bleached her tattoos and removed her piercings. Meanwhile, Olivia tells Broyles that the boy's photo has been given to Samantha Gilmore's family, but so far no one recognizes him.
Later, Walter says that based on the boy's blood-work he was likely raised, if not born, in the basement of the building where he was found. Olivia reiterates that the place had been sealed off for decades. How did the boy get there? Walter suggests that the boy may be significantly older than he appears. Then an agent comes in and tells Olivia they got another fax. The Artist is going after another victim
A woman walks a dog down a wide street as she is approached by the man from the Laundromat, the Artist. He kneels and pets the dog while looking at its owner. He has found his next victim.
At the hospital, Olivia brings the boy a bag of M&M's to entice him to eat. She tells him that as a kid she used to live on them -- but not the yellow ones, which reminded her of medicine. The conversation is interrupted by ELIOT MICHAELS from the Department of Social Services.
The two talk outside the boy's hearing. Eliot tells Olivia that since there's nothing physically wrong with the boy, he's arranged to have him moved the next day. The boy worriedly watches them, as though he knows what they're saying. Suddenly the boy's vital monitors start beeping as his blood pressure and heart rate spike. Olivia comes back and the boy returns to normal almost immediately.
As Eliot leaves the hospital he speaks cryptically to someone on his phone. He informs them that he's located "another one."
Back in the boy's room, Olivia is about to leave when the boy scribbles another message for her: "547 Marlborough."
On Marlborough Street, Charlie and Olivia have no other leads, so they split up to knock on doors. As Olivia walks down the street, someone watches her from inside a parked van. It's the Artist, his hand firmly pressed over his latest victim's mouth to muffle her screams. Olivia continues down the street, oblivious.
Later that night, Olivia and her sister enjoy a nightcap at the apartment. Rachel asks Olivia if she likes her job. She does most days, but not today. Then Charlie calls to say they've found the Artist's second victim. She was not found on Marlborough... but they found the victim's dog tied to a fence there.
Peter and Walter's hotel room. Olivia asks Walter if he knows how the boy could be coming up with these clues. Walter posits that the boy might be hypersensitive to people's emotions. So much so that he may be able to intuitively detect the feelings and thoughts of others. Similar to the manner that sharks sense bioelectric fields, and other animals sense pheromones. Walter also believes that the boy has thoughts despite his inability to communicate them, and there may be a way he can access them.
Olivia goes to the hospital to fetch the boy. On his food tray, a pile of yellow M&M's have been shaped into what appears to be a fir tree. The two leave together.
In the Harvard lab. Walter brings out the neurostimulator (last seen in "The Ghost Network"), which he'll use to translate the boy's thoughts into sound. He'll make some minor adjustments to the halo ring so it won't need to be drilled into the boy's head.
Meanwhile, Elliot Michaels discovers that the boy has been discharged from the hospital.
In the lab, Olivia explains the procedure to the boy. She tells him if he doesn't like what's happening to simply squeeze her hand. Walter has a plan to loosen the boy up. He puts an Al Green record on and begins to dance joyfully with the scary-looking neurostimulator. The boy smiles, loosens his grip on Olivia's hand, and Walter gently slips the neurostimulator onto the boy's head.
Soon thereafter, Eliot Michaels arrives with Broyles and reveals that he's not actually with Social Services, but with a classified division of the CIA Directorate of Science & Technology. He's here to take the boy so that his abilities don't slip into the wrong hands. Astrid interrupts with news: they've received another invitation from the Artist. Broyles asks Michaels for one more day, and Michaels reluctantly agrees, on the condition that after 24 hours they'll turn over the boy without a fight.
Later. Walter is reciting mnemonics, trying to remember the proper wiring sequence for the neurostimulator. Olivia says the forensics report fround blood under the fingernails of the Artist's second victim. But the blood isn't human; it's cow's blood with plastic polymers in it. Peter says he used to work at a meat-packing plant where they wrapped the cuts of beef in plastic sheeting.
Olivia arrives at a meat-packing plant. Simultaneously, Walter calibrates the language-translation apparatus that's attached to the neurostimulator on the boy's head. As Walter tweaks the dials, the computer begins to generate language-like sounds based on the boy's thoughts. But suddenly the boy begins to shiver uncontrollably, and Peter aborts the procedure. At the meat packing plant, Olivia also shivers as she questions the manager. After Olivia asks for a sample of their plastic, the manager admits that he sold some plastic to a man the day before.
Somewhere on the street, the Artist helps a woman load groceries into her car. He's found his next victim.
Olivia calls Peter to say she's gotten a sketch of the man who bought the plastic -- finally, a solid lead. Walter interrupts Peter's conversation and asks if the plant was refrigerated, because that would explain everything.
When Olivia returns to the lab, Walter explains his theory. The boy has developed an emotional connection with Olivia. He can sense and feel what she does, and he's relaying information about the crimes because he knows that information is important to her. Olivia speaks with the boy, but senses that he's mad at her for some reason. Astrid suggests that this is because he "felt" the conversation she had with Eliot, and doesn't want to be sent away. Olivia apologizes to the boy and tells him, very sincerely, that she wishes she could stop Eliot from taking him. She can't, but she needs his help anyway. The boy writes down a set of cross streets for her: York and Glenway.
A roadblock has been set up at the corner of York and Glenway. Charlie and Olivia stop and search cars. A familiar van appears, with the Artist behind the wheel. The sketch isn't a very good match to his face. Olivia asks a few questions, and then notices the air freshener hanging from the rearview mirror. It's yellow, in the shape of a fir tree -- the same design the boy made with the yellow M&M's. Olivia tells the Artist they need to check the back of the van. He punches the gas and peels out. Olivia shoots out the van's tires. It crashes into a fence, and the Artist takes off running, Olivia close behind.
Charlie checks the back of the van and finds the Artist's third victim, fortunately still alive. Olivia, now in a cemetery, searches for the Artist. He comes from around a corner wielding a knife. A struggle ensues, and Olivia takes control of the Artist's knife and stabs him dead just as Charlie rounds the corner.
At the FBI, Broyles receives a call from Olivia; she needs his help with something. Later, she stops by Boston Children's Hospital, and asks Dr. Winick for a favor.
Olivia arrives with Dr. Winick at the lab. She tells the boy that Dr. Winick is going to take him to live with a nice family. Olivia and the boy share an emotional goodbye.
At the FBI Broyles lies to Eliot Michaels, telling him the boy disappeared from protective detail.
Olivia returns home and shares a nice moment with Rachel and Ella playing Simon Says.
Dr. Winick drives down a suburban road. The boy sits quietly content in the back seat. Out the window, the boy spots a bald man in a black suit standing by the side of the road. It's a man we've come to know as... the Observer. As the car passes by, the two make eye contact, and the boy watches as the Observer fades into the distance.