A bomb blast that rips through the locker room at a gym is linked to similar bombs that killed a young employee at a big box store in 1999, blinds a father and husband in 2001 and then kills a man at a hospital in 2003. The detectives soon realize they have a serial bomber on their hands and must protect his next target before the bomber gets to him first. Meanwhile Scotty and ADA Thomas take some tentative steps in their relationship.
- Kathryn Morris as Lilly Rush
- Danny Pino as Scotty Valens
- John Finn as John Stillman
- Jeremy Ratchford as Nick Vera
- Thom Barry as Will Jeffries
- Tracie Thoms as Kat Miller
- Kim Coates as Alessandro Rossilini
- Chris Butler as Roderick Poole
- Kate Jennings Grant as Beth Ross
- Ryan Kelley as Curt Fitzpatrick
- Bob Koherr as Carl Baxter
- Timothy Omundson as Luke Ross
- Stephanie Venditto as Helen Wainwright
- Alessandro's anti-technology agenda and his troubled relationship with his married younger brother are apparently based on Theodore Kaczynski, better known as the "Unabomber". The real Kaczynski was mentioned by Joseph Shaw in the episode "Joseph".
- Rita Baxter's then-unsolved case box is visible just below Curt's case box when Curt's box is first put away.
- Wham! "Last Christmas"
- Red Hot Chili Peppers "Snow"
- Live "Turn My Head"
- The Smashing Pumpkins "Crestfallen"
- Closing Song: OneRepublic "Apologize"