At a high school reunion, man named James Bruno picks a fight with another man, Neil Sherwood, and then mysteriously dies. The team dives into the investigation and discovers that he was poisoned. And he left a bomb in a locker.
Problematically, they learn from a former teacher that Bruno had a lot of enemies. He rented a room from an old retired substitute teacher; the room was chock full of stolen property, burglarized from a number of homes in the area.
Staking out the home, they take into custody a woman they learn is Bruno's fence. She insists that Bruno was a good person, and that if he had a bomb at the reunion, someone else made him do it.
The team, going through Bruno's effect, discover that Neil Sherwood lied when he claimed that he hadn't seen Bruno since high school, and he goes on the lam. DNA on Bruno connects him to a former classmate, Katrina Cooper.
Sherwood kills himself at Katrina's house, leaving behind a confession that he and his former high school classmates, including Bruno, were each part of a sophisticated burglary ring. Katrina's husband says that Katrina was behind the bomb, but Bruno was a good person, the opposite of Katrina.
Abby discovers that Bruno had sabotaged the bomb, so it wouldn't have gone off. They eventually discover that he had a confrontation with the former teacher, who had gone to Bruno's home to apologize later. Bruno wasn't there, but his landlady, the old substitute teacher, was.
The team realizes that she wasn't nearly so batty as she made herself out to be. She saw the million-dollar painting stolen and murdered Bruno to keep it.