A serial killer is on the loose in Angeles National Forest when multiple bodies are found in the lakes and the BAU is called in to investigate. As a group of men search the lake to find missing victims, Nick is taken by the unsub. Three bodies have been found and Nick has been reported missing. Meanwhile, Reid sees that something is troubling Rossi.
The BAU determines the unsub is probably very familiar with the area, and it's going to be difficult to find him. Flashback to the unsub's childhood. His father blames him for his mother's death and tries to drown him in the lake. Nick's body is found, but the unsub's MO has changed. And the unsub isn't following a usual serial killer's agenda. Instead of getting bold and choosing stronger and stronger victims, he's choosing younger, weaker ones. Meanwhile the unsub chooses his next victim, a girl riding a Jet Ski. He sabotages the Jet Ski by removing the fuel to strand the girl in the water and then offers his help.
The bodies have been resuscitated before finally being killed, so the unsub might have a hero complex, and he wants control over the victims' deaths because he has no control over his real life. But why choose weaker victims? Rossi thinks that maybe the unsub has been weakened by an injury.
The unsub drowns the girl and tries to perform CPR on her. We see that the unsub's father did the same to revive his son after the drowning, but believed that he failed. He buried his son, but the unsub wasn't dead. The unsub seems very ill, he coughs up blood and then has to take prescription meds. The girl wasn't resuscitated. Later, the BAU finds her body with traces of blood that does not belong to her.
Rossi tells Prentiss that Carolyn has ALS and she's asked him to be there for her when she commits suicide. Rossi says he doesn't have a choice in the matter. A young mother goes to get help at a gas station after her car breaks down, leaving her son Evan alone for a moment. The unsub takes the mother.
Dr. Carroll, the medical examiner, finds out that the unsub has a blood disease, and Morgan postulates the unsub may be trying to deal with his own death by trying to kill and then reviving other people. The team figures out that the unsub resuscitates his victims after he kills them because he wants to know what they experienced after they died.
Meanwhile the unsub finds Evan and tells him that he can take him to his mother, who has been hurt. Flashback to when the unsub crawled his way out of his grave after he sees a light. He revives the mother and asks her what she saw.
Each BAU member reacts differently to the unsub's search for proof of an afterlife. Morgan is skeptical but Reid isn't so sure, since he saw a light after his experience with Tobias. Prentiss recalls that when she coded, everything was just cold and dark. Reid says the unsub has to keep his victims dead for a fairly long time, so that they can have the time to properly experience something. The unsub revives the mother but tries to drown her son.
Garcia uncovers a police report of the unsub killing his own father. Evan escapes the unsub, who is too weak to chase after him. The BAU arrive just in time to find the unsub holding a knife to Evan's throat. The unsub wants to know exactly what happens after death, but Hotch says that no one knows, and that's why humans have faith. The unsub tries to drown himself, but Prentiss revives him, and tells him that it's not his time yet.
Rossi visits Carolyn to tell her that he can't lose her twice but can't help her die. She tells him that she wants to leave on her terms, and not as a victim of ALS. She's already taken pills and Rossi wants to call 9-1-1. Carolyn says they won't arrive in time. As she dies, Rossi holds Carolyn in his arms and promises to be with her until the very end. Rossi is then shown at Carolyn's grave, which is next to the grave of James David Rossi, their son who had been born and died on April 26, 1979.