A demolition team is preparing to bring down a building after making sure it's evacuated. As they leave, one of the workers, Phil, seems to sense something. He insists on going back into the building and goes over the blueprints. He finds a hidden tunnel and the workers go down to investigate. In an ancient chamber they find a pale boy, bald, with white eyes.
Olivia wakes up to find her niece Ella eager to have breakfast and reluctant to wake her mother Rachel.
Charlie gets a call from a contact in the mayor's office and is informed that he was sent a fax. Charlie checks his own fax and finds the same thing: an artist announcing a new showing.
Olivia is making breakfast and Rachel tells her that they are considering moving to Boston. Olivia says they can stay as long as they like until they find an apartment. Charlie calls to tell her they've received a fax from the Artist, a serial killer. Olivia hangs up to prepare to get ready. Broyles calls and tells her to meet him at the Boston Children's Hospital.
Olivia, Walter, and Peter arrive and Broyles tells them how the Child was found. Walter asks for a turntable so he can play his records. They talk to Dr. Winick, the head of Pediatrics, who notes the Child is having trouble breathing. Walter contradicts her, saying the Child has adapted to a low-oxygen environment. More oxygen will cause the Child to drown, so Walter recommends they lower the oxygen content and then slowly raise the level.
In Somerville, a tattooed girl is doing her laundry when another customer makes small talk about her tattoos. The girl blows him off until she sees he's in a wheelchair. Outside, she offers to help and the man accepts her aid. Once her back is turned, he injects her with a sedative. He then pulls off to a desert spot, kills her, and starts using a saw on her body.
Winick follows Walter's instructions and the Child's breathing eases. Winick confirms the Child can speak and hear but simply doesn't know how to speak. Walter confirms that the Child probably ate rats and insects, but the vitamin deficiencies caused his baldness. Olivia introduces herself to the Child, who jumps when her phone rings. He watches with interest as she discusses the case with Charlie and writes down an address where the recent body was found. He grabs her wrist and then writes down "Sam Gilmore" upside down on her pad.
Olivia goes to the address were the girl, Samantha Gilmore, was altered post mortem and then hung up. Olivia realizes that somehow the Child knew the victim's name.
Charlie briefs the team, explains that the Artist sedates and kills his victims, then "improves" them with surgical tools and chemicals. Each time he faxes an invitation to the authorities to see his new public works. Olivia sends photos of the Child to Samantha's relatives but Broyles doesn't think anyone would recognize him. Walter has been doing research on feral children who grew up isolated from human contact. He also suspects that the environmental conditions may have acted to slow down his aging, and he may be considerably older then he appears. They get word that the Artist has sent another faxed invitation.
The Artist approaches a woman walking her dog.
Olivia visits the Child and offers him M&Ms, and says she never liked the yellow ones. She gives him one and he offers it back. She asks him if he can give her his name. Eliot Michaels from Social Services comes in and asks to talk outside. As they chat, the Child watches them through the window. Eliot says that he's arranged to have the Child moved to a facility where he can receive the treatment he needs. The Child's vitals increase and Olivia manages to calm him down. She asks for a moment along with him. As Eliot leaves, he calls someone and says they've found "another one." Meanwhile, the Child writes down a street address.
Olivia and Charlie go to the address and canvass the neighborhood. They don't find anything, but are unaware the Artist is in his van and has restrained his victim.
At home that night, Rachel notes that Olivia didn't come home the previous night. She wonders if Olivia likes her job and Olivia says that most days she does, but today wasn't one of them. Rachel starts to talk about why she's up late, but they're interrupted when Charlie calls to tell her they found the new victim, and she had blood beneath her fingernails. Further, they found the victim's dog at the address the Child wrote down.
Olivia goes to the Bishops' hotel room and Walter emerges from the bath. She asks for an explanation and Walter suggests the Child is an empath and is picking up on the Artist's emotions from a distance. Olivia points out the Child can't say anything, but Walter suggests he may come up with a way to hear his thoughts.
Olivia goes back to the children's hospital and notices the Child has made an evergreen shape out of yellow M&Ms. She provides him with clothing and takes him to Walter's lab, where Walter has found his neural stimulator. Peter points out that it might not be a good idea screwing it into the Child's skull. Walter works on a way to modify it without drilling.
Eliot is discovered that the Child was discharged from the hospital.
Olivia reassures the Child that he can call off the procedure at any time. Walter turns on his music and dances to entertain the Child as he puts the stimulator on. As they start, Eliot arrives with Broyles and demands explanations. Olivia refuses to tell him until Broyles confirms that Eliot is actually a CIA member of the science division, and they're taking custody of the Child to study him. Eliot insists they want to protect him from anyone who wants to exploit the Child, but Olivia doesn't believe him. Broyles warns they have no choice, and Astrid tells them that Charlie called to say they've received another fax. Broyles asks for one day for the Child to help them. Eliot agrees as long as they agree to turn the Child over without a fight, and Broyles agrees.
Peter discusses G.I. Joe figures with the Child while Walter tries to recall the wiring sequence on the stimulator. The forensic report comes in on the DNA report on the blood from the second victim's fingernails. It tests as cow blood with a plastic polymer mixed in, and Olivia has Astrid check petting zoos. Peter remembers when he was working at a meat packing pack and they wrapped meat in plastic.
As Olivia checks meat packing plants, Walter attaches the neural stimulator and tries to tune in the Child's brainwaves. A voice starts to come through but the Child begins to shiver and Peter stops the experiment.
Olivia is at a refrigerated meat packing plant and talks to the owner, Mr. Wu. Wu doesn't remember any employees with a violent nature. When she asks for a sample of shipping plastic, he admits he sold plastic to someone the previous day.
An older woman is carrying supplies to her car when the Artist helps her load them in.
Olivia checks in with Peter, who says that the Child started shivering. Olivia tells him she has a sketch from Wu. When Walter learns she was at a refrigerated plant, he calls her in to explain that the Child is emotionally bonded to her and knows how important solving the murders is to her. Olivia talks to the Child but realizes that he's mad at her because he knows she'll turn him over to Eliot once they've solved the case. Olivia assures the Child that she's sorry that she can't keep him, but he can sense how deeply she feels. The Child writes down two intersecting streets.
The FBI stop and search the traffic at the intersection, and check drivers against their sketch. The Artist drives up in his van and Olivia recognizes him. When she asks to see the back of his van, she notices a yellow evergreen air freshener on the rear-view window. He drives off but Olivia opens fire and the van crashes. She chases him over a fence to a nearby cemetery. He comes at her with a knife, and in the struggle she turns the knife on him, killing him.
Later, Olivia calls Broyles and asks for her help. She then goes to see Dr. Winick and brings her to the lab. Olivia tells the Child that he'll be going with her to a home where a family will take care of him. Olivia kisses the Child and wishes him well.
Eliot isn't thrilled to hear that the Child mysteriously disappeared… according to Broyles. Broyles claims the Child disappeared from his security detail, wonders how the Child got in the underground chamber in the first, and suspects they'll ever understand everything about him. Eliot just smiles and leaves.
Olivia arrives home as Ella and Rachel are playing Simon Says. Olivia joins in with them.
Winick is driving the boy to his new home when they pass the Observer on the street. The Child stares at him, and the Observer turns and walks away.