A little girl, Ruby, goes to the nurse's office at school complaining about a sore head. A quick examination by the school nurse yields a shocking discovery: large, brutal bruises across the girl's abdomen. Amaro is interrupted while giving a Career Day presentation at his son's school. He meets Benson at the hospital to help investigate Ruby's bruises.
Benson talks to Ruby, who tells her that a monster pushed her down the stairs. The detectives question Ruby's mother next, and they immediately learn that Ruby's brother is a difficult child. Fin and Rollins head to the home to speak with the nanny, Irina, who didn't see Ruby get hurt. Back at the station, the squad reviews the facts: Ruby has had a lot of injuries in the past year. Cragen decides to talk with Ruby's older brother, Henry.
Henry tells Benson and Amaro about the prior morning, when Ruby fell down the stairs. Henry is hesitant to tell the detectives anything about Irina, the nanny. Reluctantly, Henry claims that he saw Irina push Ruby down the stairs. The detectives set out to question friends and neighbors about Irina's activities. In Henry's room, Amaro discovers a box containing matches with the heads pulled off. It's a strange thing to find in a 10-year-old boy's room.
Fin and Rollins grill Irina at the station, and Irina tells them that Henry is a disturbed boy that Ruby often refers to as "The Monster." Amaro takes the lead and questions Henry's mother about her son. She reluctantly explains that Henry is a troubled boy who has had violent tendencies in the past. Henry is looking more like a likely suspect every second.
Amaro meets with Henry to ask him about the morning Ruby fell down the stairs. Henry confesses that he pushed Ruby down the stairs, but he wasn't worried about it because she stopped crying. He also says that he hates Ruby, and he wanted to see what it looked like to watch her tumble down the stairs. He's clearly a disturbed young boy. Ruby confirms the story with Benson and Amaro.
In talking to Henry's parents, Benson discovers that they have been struggling to control Henry's behavior for a long time. An interview with Henry's guidance counselor tells Fin and Rollins that he's been on a number of medications, but none have worked. They offer Henry's parents a deal: they won't press charges on Henry if the family agrees to seek psychiatric help for their son.
Henry's parents refuse to take Henry to a psychiatrist because they don't want him to be a drugged up zombie child. Benson and Rollins warn Henry's parents that Ruby is in danger, but no matter how hard they push, Henry's parents won't budge. After the detectives leave, Henry's mother heads upstairs to tuck him in, but Henry pulls a knife on her and says he doesn't want to go to bed and cuts his mother's hand.
Later that night, Henry tells Rollins that it was all just a misunderstanding. Henry's father gets frustrated, and Henry has a temper tantrum; so Rollins sends Henry's dad out of the room. Henry asks if he can hold Rollins' pistol. Meanwhile, Henry's mother crumbles under the pressure and tells Benson that she'll admit her son for psychiatric care.
The detectives take Henry to see Dr. Huang, who flew in from Oklahoma City for the case. Dr. Huang invites Henry to play with some action figures, and Henry is immediately violent with the figures. It's enough to shake Dr. Huang to the core. Later, he explains that he's only gotten that feeling from death row serial killers. In fact, reluctant as he is to do so, he labels Henry a psychopath and recommends that the boy be submitted to a psychiatric facility for serious treatment.
Henry's parents don't take the diagnosis well. His father is outraged at the recommendation, but Henry's mother knows that it's the right decision. Eventually, she convinces her husband that permanent treatment is the best option. Later, Benson gets a phone call from Henry. He says that he locked his mom in the laundry room and started a fire in Ruby's bedroom. At the scene, the fire department quickly puts out the fire. They discover that Henry started the fire with the match heads that Amaro found earlier.
Henry is nowhere to be found, but he didn't leave the building. The detectives begin scouring the apartment complex to find Henry. Fin and Rollins find that Henry has drowned the neighbor's dog in a bathtub. They also learn that Henry stole the neighbor's pistol. Amaro finds Henry in the building's playroom, holding a child at gunpoint. Henry eventually releases the child, but keeps Amaro at gunpoint.
Amaro gingerly attempts to talk Henry down, but Henry won't relinquish the gun. Eventually, Amaro offers to trade Henry's gun for his own, but Henry shoots Amaro in the chest. Fortunately, Amaro was wearing a vest and the recoil knocks Henry to the ground. Amaro is able to tackle Henry as the police rush in.
Slide #13 Back at the station, Henry shows no remorse for his actions. During the interview, Rollins is unbelievably disturbed by Henry's behavior. Henry's parents, watching from behind the glass, are equally disturbed. The detectives explain that there's no returning from what Henry did. He'll be locked away in juvenile detention for the rest of his childhood. Henry's mother asks that they be allowed to break the news to Henry. Henry pretends to be sad when his parents tell him, but his eyes are cold and emotionless.