In flashback, the team members are being interviewed individually for an internal investigation concerning Unit Chief Aaron Hotchner. George Foyet (aka "The Reaper") had been corresponding with Karl Arnold while the latter was in prison. The team discovers Foyet became dependent on medications after he'd stabbed himself repeatedly. When a pharmacist explains to JJ that one allergy medication could be replaced with another, JJ figures out there must be certain medications that Foyet takes that cannot be substituted.
After discovering where the letters originated, Dr. Reid starts to create anagrams for "The Reaper" to figure out the alias Foyet may be using, and he comes up with the name "Peter Rhea." Narrowing down the addresses on the letters along with the name and the probable name Foyet would use to pick up his medication, the team thinks they've pinpointed Foyet's location. They surround the apartment and knock on the door, but when there is no answer, the team goes in. There is a large stack of mail near the door that indicates Foyet hasn't been around in awhile. Garcia takes a look at the laptop in the home and discovers Foyet had set up an internet alert for Peter Rhea, which meant he would be alerted when anyone did a search on the name. In the home, there are also photos of Sam Kassmeyer, the U.S. Marshal assigned to protect Hotch's ex-wife and son, Jack.
The team goes to the safe house, and they find Sam Kassmeyer seriously injured, shot by Foyet. Sam apologizes to Hotchner, and it is revealed that Foyet had stolen Sam's cell phone and repeatedly called random numbers on the speed dial until he reached Haley. On the phone, he pretended to be a marshal and detailed to a terrified Haley that both Kassmeyer and Hotch were dead, so Haley and the new marshal needed to meet at her home. The mortally wounded Sam Kassmeyer dies in the ambulance on the way to the hospital.
Meanwhile, Hotch calls Foyet on his cell phone and threatens him repeatedly. Foyet responds that Haley looks good with dark hair. Haley, believing Foyet is the new marshal assigned to protect her and Jack, lets him into the house. During a frantic drive to his own house, Hotch calls Haley and speaks with Foyet. Foyet tells Haley how her ex-husband broke their deal by still trying to track him down. Therefore, he has to kill Hotch's family in retaliation. Hotch informs Jack that he needs to help his dad work the case, and so Jack goes upstairs. Haley tells Hotch he needs to tell his son how they met so Jack would still believe in love. Foyet shoots her three times as Hotch listens on the phone.
Hotch arrives at his house, enters, and discovers bloody footprints leading up the stairs. He finds Haley's body lying on the floor and sees a figure hiding behind the curtains. Hotch empties a clip into the hidden figure, who turns out to be Foyet wearing a bullet-proof vest. Foyet falls to the floor and the two men fight. Hotch beats Foyet to death, even after Foyet surrenders. The rest of the team arrives. Hotch goes to check on Jack, who had helped his dad work the case by hiding in a chest – their secret plan designed to protect Jack.
At the end of the internal investigation, the panel rules that Agent Hotchner's actions were acceptable under the circumstances.