Summary:
The season began with the return of Billy Flynn, a.k.a. "The Prince of Darkness". Early in the season, Jennifer Jareau is forced to take a promotion at the Pentagon causing her to depart the BAU, but by the end of the season finale, she tells Rossi that she is coming back. The BAU is also charged with training new cadet Ashley Seaver, who becomes a temporary member of the team, starting in "What Happens at Home", before her offscreen departure in the season finale. In "The Thirteenth Step", a story arc featuring Emily Prentiss began. She learns from Sean McCallister, a former colleague at Interpol, that Ian Doyle, an international criminal, has escaped and will probably come after her. Prentiss fakes her death and departs from the series after "Lauren", but came back during the next season
David Rossi highlight:
In "Remembrance of Things Past,” Rossi gets back on the hunt for the Butcher, a brutal, sadistic serial killer active in the 1980s and 1990s in Bristol, Virginia, when bodies killed exactly like the old victims turn up in the same area. He had investigated the case during the first murders but was unsuccessful in catching The Butcher. He was, however, responsible for stopping his killing by narrowing down the geographic profile and alerting all possible victims in the area. The case stuck with Rossi for several years afterward. He never wrote about it because he felt doing so would give the killer too much power. At the end of the episode, the killer, an elderly, Alzheimer-afflicted electrician named Lee Mullens, is caught. Upon getting home, Rossi, having suffered a writer's block earlier, begins writing his next book, presumably about the Butcher case.
Jennifer Jereau (JJ) highlight:
When the identity of Billy Flynn is discovered by the team during his killing spree through Los Angeles, JJ is forced to act as a hostage negotiator, communicating with Flynn over the radio under Hotch's direction. JJ's speech deeply affects Flynn, who decides to release his young captive, Ellie Spicer, and commit suicide by taking a couple hostage, forcing Morgan to shoot him by threatening them. ("The Longest Night")
Sometime after the Flynn case, it is revealed the Pentagon had offered JJ the position of a liaison for the Department of Defense, something she kept hidden from the team. Despite refusing the promotion twice, JJ, after a missing persons case in Maryland, is forced to take the position because of Strauss' authority, with Hotch being unable to do anything for her. ("J.J.")
At least a week later, Garcia is shown taking JJ's nameplate off the door of her old office. ("Remembrance of Things Past")
JJ became part of the BAU-led interagency task force to capture Ian Doyle and briefly became a part of her old team. In the end, she is apparently one of the few people aware that Prentiss' death was faked and is last seen handing her passports and bank account information in Paris, wishing her luck. ("Lauren")
Sometime later, she presumably takes advantage of Strauss's temporary absence from the BAU as well as the FBI's budget cuts to meet up with Rossi and tell him she's "coming back". ("Supply and Demand")
Dr. Spencer Reid highlight:
In "J.J.", Reid takes antacids from Prentiss's desk, something that she notices; she asks, "Again with the dairy?" Reid replies with, "I can't help it, I love dairy". This implies that he is lactose-intolerant but, in retrospect, could have been a cover for his headaches that were revealed later. On the jet, he is later shown to be feeling sick and went into the bathroom. When he comes out, he is wiping his mouth as if he had been vomiting.
In "25 to Life", Reid appears to be rather disheveled. His shirt is partially un-tucked, his hair was unkempt, he reads very slowly, and he is much quieter and more subdued than he had been in past seasons. The rest of the team seems oblivious to these signs.
In "Corazón", Reid is revealed to be suffering from intense headaches, and possibly hallucinatory episodes, while working the case. Throughout the episode, Julio Ruiz, a religious leader, tells Reid that he's carrying the deaths and souls of people along with him and that they're still with him and is affecting his own soul. In the end of the episode, he goes to see a doctor, who finds nothing physically wrong with him, suggesting it may be a psychosomatic disorder. Terrified of having inherited his mother's schizophrenia, he vehemently denies this and storms out of the office. Prior to this episode, Reid exhibited multiple signs of being in pain, such as gripping and rubbing his leg, rocking in his chair, cringing in pain while in the background, putting a hand over his stomach as if he felt ill, and sensitivity to light.
He appears to be well in the following episodes, though in "Coda", he is seen carrying a book about migraines. In "With Friends Like These...", Reid confides in Morgan about his problems, remarking that he only read five books the previous week. Previously in "Valhalla", Reid had told Prentiss about his headaches. By then, Reid had gone to several doctors but no one has been able to diagnose what is wrong with him. He tells Prentiss that he has not told any of the team members because he is afraid that they will make him "feel like a baby".
In "Lauren", it is Reid and Garcia who react strongest to the news of Prentiss' supposed death at the hands of Ian Doyle when he's told, he tries to run out of the room and winds up sobbing on JJ's shoulder after telling her that he "never got a chance to say goodbye".
Emily Prentiss highlight:
n "Compromising Positions", she risks her life and is nearly killed while going undercover in order to dissuade a mentally-unstable unsub who is in the company of numerous bar patrons and employees, all in danger of being gunned down. When she accidentally gets one of the unsub's facts wrong, he is provoked into shooting her, but she shoots him first, firing her pistol hidden in a purse. Prentiss then watches as he dies.
In "The Thirteenth Step", Prentiss learns from a former colleague at Interpol, Sean McAllister, that Ian Doyle, an apparently highly dangerous criminal, has escaped from his North Korean prison and gone off the grid and apparently killed a man and stole his car. Sean warned her that he might come after her and that everyone is in danger.
At the beginning of "Sense Memory", in her apartment, when the phone rings and the caller ID is unknown, Prentiss lets it go to message and listens to the recording. The caller, presumably Doyle, is completely silent and hangs up. In response, Prentiss sets up some noise-traps near all entrances and exits in the apartment, sits down in the hallway with a gun, turns off the lights, and waits.
When Prentiss returns to her apartment after a case, she finds a package by her door. When she opens the package, it turns out to contain a small, purple-white flower. There is a flashback to some time earlier when she is working in a flowerbed filled with the same flowers, apparently by a mansion somewhere in France. When authorities, presumably Interpol, arrive and drive away with her, Doyle watches her from a balcony. He calls someone and tells the other person to "stay on on top of [it]". As he is arrested by English-speaking authorities, he looks down at one of the flowers that Prentiss dropped.
In "Coda", Doyle resurfaced in D.C., confronting Prentiss and warning her that he will seek revenge on her soon before leaving. Soon after in "Valhalla", he began killing people connected to his case as well as their families. During the investigation, he kills one of Prentiss's former colleagues, Tsia Mosely. It is also revealed that Prentiss, Sean, Tsia, and two other colleagues were part of a team assembled by Interpol that profiled terroristsand helped apprehend them, codenamed JTF-12.
In "Lauren", Prentiss goes after him alone. As she attacks him and his men near The Black Shamrock, a bar in Boston at which he and Prentiss (as "Lauren Reynolds") first met. As she holds a submachine gun at his men, he flanks her and shoots her in the abdomen. She survives, wearing a bulletproof vest, and is abducted and taken to the group's HQ. She is tortured and beaten as Doyle recounts what happened after his arrest: he was taken to a prison in North Korea, where he resisted in interrogation for two years, hoping to see his son, Declan, again. When he was shown a series of pictures of Declan and his legal guardian being executed by a mostly unseen figure, he broke down completely and would remain there for another five years. Unbeknownst to him, the pictures were actually staged by Prentiss in order to save Declan from his father's life. The BAU , having found the photos, notices that the nails of the hand holding the gun are completely bitten down; Prentiss was a compulsive nail biter when nervous. Obtaining the address of the house, they conduct a stealth raid on it, killing all of Doyle's men. As Doyle, furious to learn how he was deceived by Prentiss, begins furiously beating her. She gets the upper hand and knocks him to the floor with a wooden stick. Once she drops it, Doyle grabs it and stabs it into her abdomen. Hearing the gunfire approach, he escapes and isn't seen for the rest of the episode. The BAU arrive and take Prentiss to a hospital, where they are told that she didn't survive. They all attend Prentiss' funeral. Her headstone is marked "Fidelity, Bravery, Integrity", the motto of the FBI. In the final scene, JJ is seen approaching a woman (whose face is unseen) in France and giving her passports for three different countries and a bank account in each one. The woman's hands are shown to the viewers to have completely bitten-down nails, implying that it is Prentiss, who is alive and has faked her own death in order to go into hiding from Doyle, thus protecting the rest of the BAU team from him. The rest of the team missed her dearly and struggled to cope with the loss for the remainder of the season.
Derek Morgan highlight:
In "The Longest Night", Morgan is able to rescue Spicer's daughter and kill the unsub.
In "Safe Haven", Morgan is visited by Ellie after the latter runs away from her foster family and reunites Ellie with her biological mother.
In "Lauren" Morgan was angry with Prentiss for never telling the team of her past with Ian Doyle and the extents to which she went to get his profile. However, he was also extremely worried about her and was the agent who found her moments after she was stabbed by Doyle. After it was announced that Prentiss had 'died', Morgan reacted badly and blamed himself for her 'death'.
Ashley Seaver highlight:
Seaver is first introduced in "What Happens at Home", doing FBI training when she is approached by Rossi, who asks her for assistance in the Drew Jacobs case. She accepts Rossi's request and eventually meets the BAU team. She is unashamed of admitting her father is a serial killer. Arriving at Las Cruces, Seaver is helpful in finding clues about the serial killer, including deducing that the killer's family doesn't own a pet. She then visits Drew, unaware that he is the killer as his own wife was his third victim, getting along well with his daughter. When she tells him that the family of his wife's killer will feel incredibly sorry for what has happened, Drew becomes suspicious and then threatens her with a knife. Seaver attempted to reason with Drew, telling similarities between him and her father and stated that her father's best day in his life was going to prison. However, when Hotch arrived, the BAU having discerned Drew as the killer, he committed suicide by cop. Seaver is then given a warning by Hotch for going out on her own, and Rossi comforts her in the fact that she feels that loving her father meant being vulnerable to him.
In the next episode, "25 to Life", Seaver has become a temporary BAU member as part of her training program.
She also appears in "Corazón", but does not appear in the next two episodes.
She is seen again in "Today I Do" after being made a series regular.
In "Lauren", while the BAU are searching for a rogue Prentiss, Seaver, and Rossi are on a rooftop interviewing a suspect, when suddenly he is shot and killed in front of them. Rossi, knowing they have lost their only source of information to help find Prentiss, realizes that the team aren't looking at the case properly as they all want to save Prentiss so badly. Rossi then asks for Seaver's help, as they have to depend on the team member "with the freshest eyes" since she is unbiased, having worked with Prentiss for only a few months, while the others have worked with her for five years. Seaver initially refuses, terrified, but eventually Rossi pushes her to admit that she doesn't understand why Doyle (Prentiss' nemesis) killed a child in D.C., something which later helps them in finding Prentiss. After telling this to Rossi, he tells her "That's the Agent Seaver I'm looking for."
Shortly before "With Friends Like These...", Ashley graduated from the FBI Academy (with all of the team members of the BAU presumably attending her graduation) and has officially become a member of the BAU team as a probationary agent.
In "The Stranger", she and Hotch attempt to negotiate with a serial killer when he holds his stepmother at gunpoint inside her house, but this tactic fails when Rossi gains entry to the house and is forced to shoot the unsub dead. Seaver later comforts the stepmother, saying the unsub didn't murder his victims because of her.
At some point before the events of "It Takes a Village", she has transferred to Andi Swann's team, which JJ mentions to Prentiss.