A young boy walks to school. A man who knows him pulls up beside him and offers him a ride. Adam gets in. The man leaves a bunch of balloons that say "thank you" for the boy's parents.
Watson finds Holmes has been up all night going through his old serial killer case files, he's called "Balloon man."
Holmes heard about another abduction on his police scanner last night and is waiting to be called in. His phone rings.
On the scene, he learns the perp forced the lock on the girl's bedroom window and took her, leaving balloons. Her dad was at a bodega getting wine and her mom was at an art gallery opening. Holmes notices freshly broken ivy, presumably by the girl, Marianna Castillo.
"That's good, she's a fighter," says Detective Bell.
"If little girls could actually win fights against grown men then, yea, it would be cause for great optimism," Holmes says.
Inside, Holmes is aghast to find her parents are about to do a live TV plea for their daughter. He paints the camera to stop it then explains that the children the killer kept alive the longest were directly correlated to their parents' media exposure. "The more interviews, the faster the children died," he says.
If they want their daughter back, they just have to listen to him, Holmes says.
Holmes goes through the parents' fridge and finds a bottle of wine. He confronts Mr. Castillo, knowing it wasn't labeled as bodegas do. There are two of many kitchen items and forwarded mail, so he thinks they split and got back together. There was also an incoming call from a Long Island number right before he left the house last night.
He confesses the coworker he had an affair with called, saying she was in the neighborhood. He went to the street to talk to her.
Holmes wants to talk to her, thinking she might have seen the suspect.
At the station, Captain Gregson talks to the mistress, Lori Thompson. Holmes informs Watson that in situations such as these that require his total concentration, she shouldn't talk to him unless he talks to her.
Lori remembers a car running a stop sign and nearly hitting her.
Holmes deduces that the suspect got sloppy this time, usually he chloroforms his victims and Marianna was awake to break the ivy. He thinks it was because of the sirens. On the scanner, he heard a call right before the kidnapping of a domestic dispute two blocks away. Balloon Man must have thought the sirens were for him and sped off.
Lori saw the van, it was dark brown.
Holmes, Watson and Bell head to the neighborhood to look for more clues. As she worries that he hasn't eaten all day, he explains that talking about the case as she listens helps him draw connections he might not have otherwise.
He sees a car with multiple parking tickets, meaning it's been there for days. It's been sideswiped by a brown vehicle that was previously painted blue and white. He thinks it's a decommissioned NYPD van.
At the station, Holmes assures Watson her listening is a valuable service. For a while in London he talked only to a phrenology bust he kept in his study. He named him "Angus."
They get a hit on the BOLO for the van and find and follow it. The driver takes off and they give chase. The driver gets out and runs and Bell easily catches him. The van is empty.
The person Bell tackled is too young to be Balloon Man. Holmes recognizes a birthmark on his neck and realizes it's Balloon Man's first victim, Adam.
Back at the station, Adam isn't talking. They think he might have begun to sympathize with his captor. They wonder how much he might have helped Balloon Man with his killings.
Holmes asks for permission to talk to Adam.
He tells Adam he understands the man who took him also took care of him, taught him to drive and loved him. Sherlock tells him about being bulled in boarding school and how eventually he came to feel gratitude to his bully for paying attention to him, "in tormenting me, he was attempting to correct what I knew to be wrong with myself."
He even covered for him.
He asks how Adam got a cut on his hand, he says it was from trying to open a window in his room.
Adam finally starts talking about how the man cares for him, evening bringing him donuts every morning. Gregson interrupts the interview, Adam's parents called a lawyer for him.
Adam's parents know the police suspect him. They're trying to get him immunity with the DA.
Holmes pulls Gregson aside and suggests that from what Adam said he now knows Balloon Man works nights.
Holmes goes home with his old case files, determined to stay up all night. Waston offers to help. She shows him a squat exercise to help him stay awake.
In the morning, Holmes wakes Watson up. The early victims had all had their houses fumigated, but when the FBI checked into the employees, none were suspicious. Holmes thinks Balloon Man changed jobs. Recent victims' families or neighbors all had subscriptions to the same business newspaper.
He gets the delivery man's name from the company. Samuel Abbott.
Holmes and Watson wait in the van as teams bust into Abbott's apartment. It's totally empty, without furniture.
But there's a bunch of balloons for the police that say "Congrats!"
There's a flash drive attached.
It has a recorded message from Abbott, confessing to killing six people and saying if he doesn't get his "son" Adam back by tomorrow, he'll kill Marianna.
Gregson catches the Castillos up on things. Mrs. Castillo asks Adam, who is 19, what he wants. Holmes points out that abuse victims are sometimes protective of their abusers, but it doesn't mean they should be reunited with them.
Gregson tells Holmes that no one with the NYPD can talk to Adam. Holmes asks where he is.
Waiting for Adam, Holmes thanks Watson for being willing to put up with a "difficult person with a difficult process for the greater good." He says he may even listen to her again in the future.
Holmes talks to Adam again. Adam calls Abbott his "dad." Holmes knows Adam loved him, but he didn't love what he did. Adam is confused and doesn't know what to do.
He asks Holmes if he signs the deal, will it make up for the things he's did. Holmes says no, he can never get their blood off his hands. "But that doesn't mean you shouldn't try," he says.
Adam agrees to sign the paper and tell them where they live.
They bust in on Abbott at the table making a sandwich for Mariana. He grabs her when they bust in, threatening to shoot her. Instead, he tells them to tell Adam he's sorry. Then he shoots himself in the head.
Later, Holmes stands over his dead body. He's more feeble than Holmes expected, and wearing a back brace after multiple surgeries. He would have needed Adam to help him get around.
There's a dingy twin mattress on the floor and a real bed in the bedroom.
Holmes hears a whistling noise and finds a broken window in the bedroom. He snaps a picture of a hair on the bed.
Then he announces Samuel Abbott is not the Balloon Man.
Holmes waits for Adam in his bedroom, he snuck in through the window. He reminds Adam that he said he cut himself on the window in his bedroom. He knows the bedroom with the lamps, mattress and TV was Adam's room, Samuel slept on the dingy twin mattress. He confirmed it by matching the hairs on each.
"You occupied the master bedroom because you were the master," Holmes says.
"You tricked me, Adam, which doesn't happen very often. I thought you were a dullard. You're actually quite brilliant. It must take a huge intellect for a boy to turn the tables on the man who abducted him," Holmes says.
"You have no idea," Adam says smugly. Holmes asks whose idea it was to take more children. "I'd just turned 14, I was lonely," Adam says.
"No, what you wanted was to make someone else the victim, hurt them like you'd been hurt," Holmes says.
Adam remembers seeing his parents on TV at least once a day after he was abducted. He enjoyed it. Turning the tables on Abbott was easy, given his low IQ.
The trade for Marianna was Adam's contingency plan in case he got caught. He knew the police would offer him immunity.
"Are you here to kill me, Mr. Holmes? Because I have to admit I find the possibility very exciting," Adam says.
He announces he's going to brush his teeth and doesn't expect to see Holmes when he returns. He's thinking of leaving town soon.
Back at his house, Holmes throws knives at Adam's immunity deal, which spares him from prosecution for any crimes committed "in consort" with Samuel Abbott.
"I handed a psychopath a get-out-of-jail free card," he says.
Watson suggests Holmes try more squats instead of throwing knives, but he did too many and his back hurts. He has a back pain epiphany.
Holmes goes to find Adam in a park, watching a family with a young child. He asks about his fifth victim, Billy. They just ran the DNA under Billy's fingernails and it wasn't Abbott's. Holmes mentions the date of the abduction, the same time Abbott was in traction in the hospital for his back surgery. The deal only covers murders committed with Abbott.
"It was only one murder, and Samuel abused me. I'll be out soon," Adam says as police cars pull up for him.
Back home, Watson closes the blinds saying it's time for Holmes to sleep. He thinks he'll see everything with a new light on his solving high. "I'm going to solve three cases by nightfall," he boasts.
Watson steeps tea. When she turns around, Holmes is asleep on the floor.