Principal Givens finds a bomb in the clock in his home, and an unsub walks up behind him and shoots him in the leg. When he tries to dial 9-1-1 on his cell phone, the bomb in the clock is activated and explodes.
Back at Quantico, Garcia presents the case and they find out that the bomb had been modeled after the one Randy Slade had used 10 years earlier when he went on a killing rampage in the school cafeteria.
The team reviews information on Randy. They go talk to Randy's younger brother, Brandon. Rossi talks to Brandon about being bullied in school, and Principal Givens not standing up for him. Brandon insists he has an alibi. Prentiss finds a list of names in Brandon's room. They investigate the connection they have to each other. They think that Brandon might have a partner. Prentiss talks to the students on the list, but he doesn't get any leads. Garcia analyzes the list: one group is of popular kids and the other is of loners. Garcia thinks it might be someone not on the list, and suspects Lewis Ramsey.
One of the original survivors, Jerry Holtz, tells Prentiss how he had provoked Randy in the cafeteria, and Randy told him he wasn't worth one of his bullets so he pulled out a bomb. Jerry also tells Prentiss that Randy's cell phone is grey, and was used to activate the bomb. The cell phone was black. Lewis insists that he didn't kill Chelsea.
Back at school, Lewis is viciously attacked and murdered.
After some investigation, Reid discovers the unsub is unable to feel pain, physically or emotionally. This condition, called asymbolia, can be caused by severe trauma, such as a bomb explosion. JJ looks at the list some more and he realizes what it is.
The team realizes the only tie between the new victims and the previous victims is something called the Top 10, which JJ determines is the group of survivors who were hand-picked by Principal Givens to appear on the media circuit to talk about the massacre. The unsub is angry because he had been excluded from the Top 10 as he was the only person to stand up to Randy Slade. He wanted the glory that had been denied to him after the original massacre.
Garcia identifies the unsub as Robert Adams, who's at a restaurant where the remaining survivors, the Top 8, are gathered. He sets off a bomb before he enters with a gun.
Prentiss and Hotch enter the restaurant where Robert has gone to confront the remaining survivors. Hotch confronts Robert and shoots him.