The episode begins in Brooklyn and the year is 2005, where a boy named Adam is walking to school. A car pulls over and a voice calls out to him. Sounds like, Adam has seen this guy before! He offers Adam a ride and Adam notices lots of ‘thank you” balloons in his car. The man tells him that they are for his parents. Adam gets into the car and the man leaves the balloons on the site where he picked up Adam. Cut to the present, Holmes is looking at some old case files of the Balloon Man. He tells Watson that he heard on his police scanner that the Balloon Man has abducted one more girl named Mary Ann last night and he will be receiving a call from the PD soon.
His phone rings and Holmes arrives at the victim’s house. Gregson tells him that the perpetrator had broken into the girl’s bedroom through the window and took her leaving the balloons. The father was at the bodega buying wine and the mother was at the opening of an art gallery. Holmes notices some freshly broken roots and assumes that the girl must have broken it on her way out for as a hand hold. Bell thinks she is a fighter. They go inside the house and see that the parents are about to give an interview to a news channel. Holmes takes a spray paint and paints the camera lens. He had warned the cameraman against recording.
He then tells the parents that the Balloon Man thrives on the mourning of the children’s’ parents. The more the media exposure about the case, the earlier the Balloon Man would get rid of his victims. This he found out when he studied the earlier cases and co-related it to the media exposure. So, he tells the parents to do as he says; and he is right most of the times; almost every time. Holmes then examines the kitchen and goes through other things in the house. He arrives and tells Mr. Castillo that he is lying as he did not buy the wine from the bodega as it is labeled differently. There are too many kitchen items, which prove that the couple has separated and got back again.
Also from his mails and caller id, he figures out that Castillo has a mistress and he had gone out to meet her last night when Marianna was abducted. He admits to meeting his girlfriend and Holmes tells him that he wants to talk to her as she could have seen something. At the station, Gregson talks to the mistress Lori Thompson. Lori then tells them that she saw a van running a stop sign and nearly hitting her. Holmes thinks that the Balloon Man got sloppy this time as he usually chloroforms his victims but Marianna was awake when he took her. He also mentions hearing sirens when he was listening into the police scanner.
There was a domestic dispute two blocks away from Castillo’s house and a cop car was dispatched to settle this situation. So the Balloon Man must have heard the siren, thought it was for him and panicked and then sped. Lori tells them that the van was dark brown. Watson is worried that Holmes has eaten the whole day. Next, bell, Watson and Holmes go to the neighborhood and find a sedan with a lot of parking tickets, which means it has been there for days. He also notices that it has been sideswiped by a brown vehicle. But there are also white and blue paint mixed with the brown. Holmes infers that this van is a former decommissioned NYPD van. He asks Bell to do a BOLO on this van.
Gregson and Bell tell Holmes that they got a hit on the BOLO. They find the vehicle and chase it. a man tries to get out and run but bell easily tackles him. The van is empty. Bell takes off the hood and tells Gregson that this guy is too young to be the Balloon Man. Holmes looks at a birthmark and declares that this boy is the first victim; Adam. They interrogate Adam but he refuses to speak. Watson tells Holmes and Gregson about a case she read about where the victim grew sympathetic to his captor and inadvertently helped him. There is a possibility that the same happened with Adam and he could have helped the Balloon Man with his other victims; to what extent, that can’t be said but Adam could help them find Marianna.
Holmes wants to talk to Adam and Gregson after a bit of reluctance allows five minutes of questioning. Holmes enters the room and introduces himself. He then tells Adam about a bully at the boarding school who tortured Holmes a lot. But instead of hating him, Holmes says that he liked the attention he got from his tormentor. Adam begins to open up to him and tells Holmes that the man loved him and took great care of him. Just then Gregson arrives and says no more questioning as Adam’s parents have lawyered up. They know that the police suspect Adam and so they are trying to get immunity from the DA. Holmes says that after talking to Adam it is clear that the Balloon Man works nights.
He then decides to stay up the whole night going through old case files and Watson shows him a squat exercise to stay awake. The next morning, Holmes wakes up Watson and tells them that the earlier victim’s houses were fumigated and the FBI came up with a theory that the Balloon Man was an exterminator. But they did not find anything concrete and so they discarded the theory. He then shows her pictures from the house of victim number three and points out to the subscription slips. They were the same newspaper that Holmes had seen in Castillo’s and the neighbor’s houses. So, the Balloon Man who was an exterminator now delivers papers at night for the investor’s post.
He is now talking to the newspaper agency and gets a name; Samuel Abbott. Next, the cops bust into Samuel’s apartment and they find it empty. But there find a bunch of balloons which says “congrats’. Holmes says that it is for them for finding his house. They then see a flash drive on the balloon. They then play a video in which Samuel admits to his six killings and tells them that if they don’t return his son Adam by noon the next day, he will kill Marianna. Mrs. Castillo wants the trade to be made. But Gregson says that this cannot be done as Adam hasn’t signed the papers. Later, Gregson tells Holmes that the order from the court says that no cop can talk to Adam; this means Holmes can.
Holmes talks to Adam once again and Adam tells him that he loved his ‘dad’ Samuel. But Holmes points out that he did not like what his dad did. Adam tells him that he is confused and doesn’t know whether he should sign the immunity. Later, he decides to sign the papers and tell the cops where they can find Samuel and Marianna. Next, the cops bust into Samuel’s apartment and Samuel grabs Marianna, threatening to shoot her. then he tells the cops to tell Adam that he is sorry and shoots himself. Holmes looks at the dead body and thinks that this man is feeble and is wearing back braces due to multiple surgeries. He definitely required Adam’s help to get around.
He then hears a whistling sound. He sees that there is a small, dingy room with a mattress and a master bedroom with a broken window glass. Holmes is shocked. He then photographs a hair on the pillow in the master bedroom. He then declares that Samuel Abbott is not the Balloon Man. Next, Holmes waits for Adam in his room. He knows that Adam is the Balloon Man. He remembers that Adam told him that the wound on his hand was from trying to open the window with a broken glass in “his” room. Adam occupied the master bedroom; indicating that he was the master. Adam admits to his crime but seems proud about it. He says that it was easy to turn tables around on his abductor as he had an IQ south of 90.
The trade for Marianna and the immunity was just in case if Adam got caught. But he has immunity and so law cannot touch him. At home, Holmes is pissed that he managed to give a psychopath a get-out-of-jail-free card. Watson tells him to exercise and he tells her that his back hurts. Just then he gets an idea. He then meets Adam in a park. He tells Adam that his immunity is for crimes he committed “in consort” with Samuel; but Adam’s fifth abduction of Billy was done by Adam alone as Samuel was in the hospital during those days for his back surgery. So, Adam can be prosecuted for murder. The cops arrive.
At home, Watson shuts the doors and windows so that Holmes can get some sleep, but he says that he is going to solve three cases by midnight. She then prepares tea. When she turns around, Holmes is lying on the floor; fast asleep. The episode ends.