After a missing FBI agent turns up dead, Pierce is forced to face the one case he was never able to solve. When they discover that the killer is still out there, Pierce agrees to help Moretti, against the wishes of his therapist, Dr. Rosenthal, who believes it will only exacerbate Pierce's condition.

When Donnie finds himself in a compromising situation, he calls Pierce for help. As the evidence begins to stack against Donnie, Pierce and Moretti struggle with their own fears and doubts, as they work to solve the case. During the chaos, Pierce must deal with his father after he assaults someone at the assisted living facility.