Two Phoenix police officers are on patrol and discussing sports, when the senior officer asks his partner where they are. When the rookie officer replies doesn't he know, his partner slams on the brakes at an intersection and explains the importance of always knowing where you are.
They receive a domestic violence call at 4129 23rd Avenue. When they arrive at the scene, the senior officer enters the house while his partner returns to retrieve his flashlight. While the younger officer is at the car, the unsub comes up behind the senior officer and shoots him. The younger officer calls for backup before drawing his gun to shoot the unsub, but he is killed by the unsub before he can fire.
At a press conference with the Phoenix Police Department, the officers are identified as Manny Rodriguez and Tom Kayser. Their deaths made a total of three murdered cops in four days, according to Agent Todd, and Commander Marks had asked for the FBI's help. As the team discusses the case, it is determined the unsub is taking his victims' badges as a trophy. The first victim had been Officer Kessinger, and the unsub had used a DUI check to lure the officer into his trap.
Garcia informs the team she has been having trouble getting any information from the Phoenix officers because they are unhappy the bosses have called in the FBI. She warns them to be ready to face the "blue wall of resistance."
The team is introduced to Lt. Evans, whose animosity towards them is obvious. Commander Marks calls Hotchner into his office to apologize for bringing them down, as further investigating on the police department's part has led him to believe the killings had been committed by gangs. Hotch explains to him that, although he understands why they may see it that way because the officers had been killed with different weapons, his team believes this to be the work of one person with access to multiple weapons. Additionally, it is unlikely gang members had committed the murders because planning went into the murders and the killer is taking trophies.
Commander Marks explains to Hotch that his back is against the wall because his officers feel betrayed and they view his asking for the FBI's help as a lack of faith in their ability to catch the murderer. Hotch acknowledges Commander Marks' concerns, and explains they are there to work with the officers and not take over the investigation. He goes on that if this is the work of one unsub, then he is likely looking for a new target, and the sooner they can get a profile, the better chance they have of catching him before he kills again.
Lt. Evans takes Morgan and Prentiss to the scene of the second shooting, where he tells them he believes that one gang, the Twelves, are behind the murders. He tells them about the Twelves' captain, Playboy. Apparently Vice had broken up a drug ring that had resulted in the death of Playboy's brother, who had vowed he would kill them all. Morgan and Prentiss explain, while that is possible that this is revenge, it is not likely. The unsub chose this neighborhood because he knew that the neighbors were accustomed to hearing gunshots and would be unlikely to call the police.
Back at the precinct, Hotch, Reid, Todd, and Commander Marks review the dash-cam recording from the slain officer's car. From the video, they ascertain the unsub gains confidence from each kill.
Officer Cunningham and Officer Mercer are called to the scene of a burned-out car in a parking lot, where they discover what appears to be a person lying next to the car and someone standing over the body. When a fire is ignited, they rush into the lot. One officer uses his extinguisher to put out the fire only to discover that the "body" is actually a mannequin. Meanwhile, Officer Mercer searches for the suspect without realizing they have entered a trap. As he corners a building, he is shot. His partner calls for back-up, and takes fire as he tries to get to his partner. Officer Cunningham dies at the scene and the unsub escapes capture.
Morgan interviews Officer Mercer regarding what had happened. Lt. Evans still believes Playboy was the culprit, and goes so far as to say it had been him at the scene, although as Officer Mercer had not seen the unsub.
Morgan explains to Prentiss and Rossi that the unsub is apparently selecting his victims at random because he could not have known these two officers would have responded to this scene because they had just been assigned to the beat.
Morgan, Prentiss, and Rossi realize the press will not be their only obstacle in this case because the officers still seem to think the Twelves gang is behind the attacks.
Lt. Evans arrests Playboy and takes him back to the precinct. Playboy still maintains his innocence. The team explains this action was not a good idea because bringing in the wrong suspect might aggravate the unsub and force another attack sooner and cause the gangs to lash out because their captain had been brought in.
Morgan interrogates Playboy and tells he knows he didn't do it, but he feels he knows who did. He caters to Playboy's ego, and tells him the unsub is making him look foolish by having him brought in for something he didn't do. The discussion continues as Morgan attempts to jog Playboy's memory. Playboy thinks about it and then recalls a man who had killed Playboy's lieutenant. Lt. Evans undermines the interrogation by insulting Playboy, and Morgan has to redirect the interview back to the unnamed suspect. Playboy tells him he doesn't know the man's name; however, if he did know, he would be dead already.
Hotch steps into the interrogation to advise Morgan and Lt. Evans that there has been another shooting. Morgan remains at the precinct and continues the interrogation with Playboy, confident that Playboy knows something.
Rossi and Prentiss tell them they have a shooter cornered. The shooter is a gang member named Diablo. Hotch and Prentiss talk to the victim, Sergeant Dawes, who is being placed in an ambulance. They learn the officers had not been called to the scene this time; it had been a blitz attack. The shooter is killed, but Hotch still isn't convinced this is their unsub. Hotch asks Commander Marks for another 24 hours on the case, and the commander gives him four.
Morgan asks for Lt. Evans' help in finding more information on Playboy's murdered lieutenant, Bobby Q. Further investigation leads them to believe that Bobby Q's murder was one of their unsub's first kills. They identify a few more murders and realize as the unsub's confidence escalates, so does the implied strength of his victims (i.e., bouncers, gang members, and then police officers).
From Playboy, they learn the unsub may have attended a fight club, and losing a fight is likely the stressor that had pushed him over the edge. The police and the BAU arrive at the scene of a fight club, and threaten to take all involved to jail unless they cooperate. After questioning the fight club captain, Beanie, they learn one man, called Animal, had lost every fight. They take Beanie in so he can provide a composite sketch.
To redirect the unsub's attention away from the police officers and place it on himself, Hotch holds a press conference to announce the FBI is taking over the investigation. After the press conference, they explain to the officers that issuing the press conference in this manner issues a challenge the unsub can't resist and will target Agent Hotchner in the next attack.
When a call comes into the tip line and an address is provided to the police operator, it is determined this is likely an attempt by the unsub to lure them into his trap. They set up to take the unsub down at the address. When they into the apartment, they learn it had been a false alarm. The teams are split up and warned to be on alert.
Hotch returns to the precinct. The unsub had followed him and tries to catch him unaware. However, this maneuver had been predicted. Hotch, Morgan, Prentiss, and Rossi apprehend him. As they are taking the unsub into the precinct, Playboy steps out of the crowd and shoots him, killing him on the scene.
Morgan tells the rest of the team to go ahead and he stays behind to attend Officer Mark Cunningham's funeral. He speaks with Sam, the officer's young son, and tells him not to forget that his father had been a hero.