The darkest parts of her past come back to haunt her over the course of several episodes in season 6, when she is stalked and eventually confronted by a former nemesis. In "The Thirteenth Step," she meets up with a former Interpol colleague, who gravely informs her that a man named Ian Doyle has escaped from prison. Emily, visibly shaken by the news, asks, "Am I in danger?" "We all are," he replies.

In "Sense Memory," Emily comes home from an assignment to find her bedroom window open. Though she eventually discovers that it was just left open by the housesitter, Emily isn't taking any chances. She turns out all the lights, puts her hallway table in front of the door with a vase poised to fall off if anyone jars it, and spends the night sitting in a chair facing the door, holding her gun. Throughout the episode, she is testy with Morgan and won't tell him why she is acting strangely; at the end of the episode, she arrives home to find a box of flowers and a message from Doyle. Emily grabs her cat and abandons her apartment.

In "Today I Do" and "Coda," Emily's background begins to come to light. She bands together with two former colleagues, and the three discover that Doyle is murdering everyone who helped put him away, which means all of them are on his list. Afraid to put her BAU friends in danger, Emily keeps all of this from them, even as Doyle confronts her in public and calmly tells her, "You took the only thing that mattered to me. So I'm gonna take the only thing that matters to you: your life." He lets her know he's got an eye on every member of her BAU team and won't hesitate to take them out if she tries to involve them.

In "Valhalla," Doyle's killing spree catches the eye of the BAU as he murders, one by one, not only the agents who put him away but their families, too. Emily realizes she will have to stop Doyle on her own in order to protect her own "family," the BAU. At the end of the episode, she mournfully gazes at each member of her team and then slips away unnoticed during a briefing, determined to bring Doyle down even if it kills her.

But the BAU isn't far behind her. In "Lauren," Hotch and the others put the pieces together and figure out that Doyle's intended final victim is Emily herself, who had operated under the name Lauren Reynolds. When they find out that she has gone AWOL without her badge and gun, Hotch declares her a victim and Doyle an unsub, and he summons JJ (A.J. Cook) from the Pentagon to help find Emily before it's too late.

In profiling Emily, the BAU uncovers some surprising and uncomfortable information. Before coming to the BAU, Emily was actually CIA, assigned to an international task force to profile terrorists. Each member of the team came from a different governmental agency and was the best and brightest in his or her field. Doyle was their last case. But the CIA, as JJ points out, utilizes a technique the BAU doesn't: infiltration. "Emily was his type," she explains to a stunned gathering of the team. As Lauren Reynolds, in other words, Emily had to become Doyle's lover. Morgan, in particular, is appalled and nurses a strong sense of resentment at being kept in the dark. To his mind, he has fought alongside this woman for five years yet knows nothing about her.

In the meantime, Emily has tracked down Doyle to Boston, but he's ready for her; he captures her and takes her to a warehouse, where he burns a shamrock-shaped scar into her chest and expresses plans to kill her as soon as she's "confessed." We learn, through flashbacks, that he fell in love with Emily/Lauren to the point where he gave her a gimmel ring, tantamount to a marriage proposal. But we soon discover that his sense of betrayal goes far deeper than their relationship. When she was with him as Lauren, he let her in on his biggest secret: his 5-year-old son, Declan. Doyle then asked her if she would raise his son to be a "warrior" like him. Emily/Lauren, who had grown fond of the boy, was appalled at the idea of helping Doyle corrupt his son and replied that she would do a lot of things for him, but not that. Later, Doyle's North Korean captors demanded that Interpol give up more information on him so they could break him. They were given pictures of Declan bound and shot in the head, execution style, with some unidentified person's hand holding a gun. "They laughed at me while I wept," Doyle savagely recalls.

To get his revenge, Doyle now prepares to execute Emily; he drags her roughly over to a wall and holds his gun to her. But she tells Doyle there is something he doesn't know about those photos. When she was asked to give up the additional information, she feared the North Koreans would find a way to use Declan. "I wouldn't let him be a pawn--the things they would have done to him to get you to talk. But I knew, even if I didn't cooperate, they were gonna find him eventually. So I had to...I had to end his suffering before it could begin." What she did was to stage a fake execution, then secretly relocate the boy. Livid, Doyle screams, "He's alive?" and brutally beats and kicks Emily, who gasps out, "Just because I held a gun to him doesn't mean I shot him. I only had to make you and the North Koreans believe he was dead."

Meanwhile, the BAU have discovered the photos, recognized Emily's hand holding the gun (via her chewed-up fingernails), and made the connection. They also track down Emily and Doyle's whereabouts and surround the warehouse with a SWAT team. Inside, Emily has gotten the upper hand. With Doyle in a chokehold, she laughs at him, saying, "I beat you, Ian! Before you even got out of North Korea, I beat you, because I gave Declan his life back." But at that moment, the SWAT team cuts the power, distracting her. Doyle overpowers her and they struggle, crashing into a wooden table. Emily seizes one of the broken table legs and whacks him repeatedly across the face, then drops it to get the gun he had dropped earlier in the scuffle. But Doyle grabs the table leg and impales her on it. Emily gasps in shock and collapses; Doyle, himself badly injured, crawls over to her and softly asks, "Where is he? Where's Declan? Emily, tell me where he is." To which Emily whispers, "No..." But the team has infiltrated the warehouse, and Doyle barely has time to escape before Morgan bursts in.

Morgan shouts for paramedics. His sense of betrayal gone, he tends to Emily and tries to keep her conscious. "Let me go," she moans. "No, I will not let you go," he tells her. "Listen, I know why you did all this. I know what you did for Declan. I am so proud of you. Do you understand that? I proud of you because you are my friend and you are my partner." As she slips away, he begs her to squeeze his hand if she can hear him. Later, the team waits endlessly in the hospital until JJ enters and somberly announces that Emily never made it off the operating table. As the others break down, she steps into the corridor and speaks with Hotch. Though we can't hear their conversation, JJ appears to tell him, "We did the best we could," to which he bleakly replies, "I know." A funeral is held, with Reid and Morgan among the pallbearers. Each member of the team places a rose on the casket, and then all of them form a protective ring around it. Morgan and Garcia hold hands; JJ and Hotch exchange significant glances with each other.

Some time later, at a café in Paris, JJ meets a mysterious woman who is only shown from the back. She offers the woman passports for three different countries, as well as bank account numbers to keep her comfortable. The woman, who has Emily's telltale bitten fingernails, thanks her; JJ tells her, "Good luck", and the woman disappears into the night.

We later learn that Emily's surgeons had actually managed to save her life and that Hotch and JJ had decided to fake her death to protect her from Doyle ("It Takes a Village"). Still critical, Emily was airlifted to Bethesda under tight security while the team was being informed of her death. She then stayed at Bethesda until she was well enough to travel, at which point she was assigned to Paris under an assumed name. In the ensuing months, Hotch and JJ kept up a front, with Hotch going so far as to give grief counseling to Reid, Garcia, Morgan, and Rossi ("Hanley Waters"). Morgan took her apparent death particularly hard, feeling she would have lived if he had just arrived sixty seconds earlier. In fact, so great is his guilt and outrage that he spends all his free time hunting down Doyle.

Key episodes:

2x09: "The Last Word"
2x10: "Lessons Learned"
2x11: "Sex, Birth, Death"
2x16: "Fear and Loathing"
2x20: "Honor Among Thieves"
2x21: "Open Season"
2x23: "No Way Out II: The Evilution of Frank"
3x04: "Children of the Dark"
4x03: "Minimal Loss"
4x17: "Demonology"
5x11: "Retaliation"
6x13: "The Thirteenth Step"
6x14: "Sense Memory"
6x15: "Today I Do"
6x16: "Coda"
6x17: "Valhalla"
6x18: "Lauren"
7x01 "It Takes a Village"

Who is Prentiss? Discuss her character development by season.

Season 1	Prentiss did not appear until Season Two.
Season 2	Episode 2x09 "The Last Word" This is the episode that the then-SA Emily Prentiss first appears on the show. She is the daughter of a high-powered diplomat, Ambassador Prentiss, whom Hotch worked with early on in his FBI career. For reasons which are unclear, she has paperwork to join the BAU, but neither Hotch nor Gideon was aware of it. Hotch is wary of her, but at the end of the episode, he reluctantly agrees to take her onto the team on a probationary basis. Episode 2x10 "Lessons Learned" is Prentiss' first full episode. In it, we discover that she spent considerable time in the Middle East as a child, traveling with her parents, and is well-versed in the Arabic language and culture. This is the first episode where Prentiss really proves that she has potential as a profiler, picking up on the subtleties within the words and actions of their suspect. Episode 2x11 "Sex, Birth, Death" Hotch believes that Prentiss leaked details of their case to a congresswoman who worked with her mother, an accusation which she resents. It becomes fairly clear to Hotch and the viewers that Prentiss harbors a strong dislike of politics. This is also the first sign we've seen that Prentiss doesn't like her mother. Episode 2x13 "No Way Out" Prentiss clearly bonds with Jane, a mentally ill woman who the serial killer they're tracking seems to be obsessed with. No explanation is given for this bond. Episode 2x15 "Revelations" Both JJ - dealing with the trauma of Reid's abduction - and Hotch question how Prentiss can handle the horrors of their job so easily after working a desk job. Prentiss, clearly put out, responds that she "compartmentalizes better than most people." Episode 2x16 "Fear and Loathing" Prentiss and Morgan bond over their shared love of Kurt Vonnegut. Prentiss tries and fails to cheer Morgan up when the head detective on the case is shot. At the end of the episode she makes a potentially significant, though probably meaningless, slip of the tongue, saying she hasn't read Kurt Vonnegut's Mother Night in, "Fif-- like, twelve years." Episode 2x17 "Distress" marks something of a breakdown of the Reid and Prentiss's friendship. Up until "Revelations," Reid had been friendly to Prentiss -- more-so than anyone else on the team. In "Distress," as a result of his own trauma and, to some extent, Prentiss' unwillingness to let his strange actions slide like the rest of the team, Reid snaps at her several times, and they spend the entire episode -- and some subsequent ones -- on uncomfortable terms. In this episode, we also find out that Prentiss speaks fluent Spanish. Episode 2x18 "Jones" Prentiss' relationship with Reid, and the team, progresses even further. When Reid misses a flight intentionally, Prentiss is tempted to express her doubts about him to Gideon, only to find that Gideon is having the same doubts. Episode 2x20 "Honor Among Thieves" is largely about Prentiss. Her mother comes to the BAU and asks that they take the case of a Russian man who has been kidnapped by the Russian mob, or so his family thinks. Ambassador Elizabeth Prentiss used to work at the Ukrainian consulate, and Prentiss knows a good deal of Russian. Prentiss' relationship with her mother is clearly strained, from their interactions in the episode, and notably her father is not mentioned. Prentiss states that she has never seen her mother with her guard down. Episode 2x21 "Open Season" is also somewhat Prentiss-based. In the opening scene, she, JJ, and Garcia trick a man who is pretending to be an FBI agent to pick up girls at a bar. At the end of the episode, it's clear that she identifies with the victim, Bobbi, who asks her how unsubs can act the way they do. Prentiss says that the unsubs don't think like them, but later, on the plane, she confides to Morgan that they do. "What makes us different?" she asks Morgan. Episode 2x23 "No Way Out II: The Evolution of Frank" Jane, from Episode 2x13, returns, and once again, Prentiss's bond with her is clear. At the end of the episode, Erin Strauss, a Section Chief in the FBI, wants to get Hotch off the team. She tells Prentiss that she pulled strings to get her into the BAU, and that she can get her off the BAU if she doesn't spy on Hotch. We don't see Prentiss' response.
Season 3	Episode 3x02 "In Birth and Death" Prentiss resigns, until Hotch tells her he knew that she didn't report anything negative about him to Section Chief Erin Strauss as she had asked. He informs her that her resignation isn't in the system yet so they are bound to help the team in this case, which is later found to be Garcia's doing. Prentiss puts herself in harm's way when she knocks on the door of the unsub's home and his son lets her in. She is armed with Morgan's gun and convinces the boy she knows the father and he invited her over. She finds out where the father is and goes into the room where he is holding his latest victim, the school nurse, hostage. He clubs Prentiss on the head with a piece of wood and hands his son the gun and tries to get is son to shoot Prentiss. Prentiss is disoriented but manages to send the signal out via her cell to the team to come in. She is okay and announces "is it wrong that I am happy to be back?" to Hotch. She returns home and reflects from her window in her apartment. Episode 3x03 "Scared to Death" Prentiss chats with Reid about why Gideon left him the letter for his reasons for leaving. Reid was trying to understand it and Prentiss tells him the answer is in the letter and to reread it. This is one of the first moments where we see the relationship between Reid and Prentiss fixing itself since they had their falling out following "Revelations". Episode 3x04 "Children of the Dark" A teenage girl survives a brutal and fatal attack on the rest of her family, and Prentiss bonds with her after the girl says it's too late to be a good daughter now that her parents are dead. Feeling the girl has no family and nowhere to go, Prentiss offers to bring her home with her to live and take care of her but the girl's extended family comes forward, leaving Prentiss feeling a little lost. JJ tells her on the plane that she can see that she would make a good mother. Episode 3x05 "Seven Seconds" The BAU team races against the clock to find 6 year old Katie Jacobs who was kidnapped from a mall. Prentiss really steps up as she interviews Susan and Richard, the aunt and uncle of young Katie. After she and Hotch interrogate Richard, they discover he'd been molesting Katie. Hotch points out to Prentiss that the uncle showed no rage and the act of ripping off Katie's necklace had been done in rage. She thinks back to her conversation with Susan and realizes that she was behind Katie's disappearance. She interrogates her until she breaks, and then arrests her after Katie is found.
Season 4	Episode 4x03 "Minimal Loss" Reid and Prentiss go undercover as child services employees to a ranch/cult where they are held captive. After a press leak that an FBI agent is in the compound, she willingly gives herself up as the agent and is subsequently beaten by the cult leader, Benjamin Cyrus. She endures the beatings and is able to get one of the women in the compound to confess that she made the initial call that brought them there. Prentiss also convinces the woman to get most of the remaining captives into the basement before the building was to be raided. In the end, Prentiss plays an essential part in getting the case solved. Episode 4x09 "52 Pick-Up" Prentiss atracts a creepy 'how to get a date' guy named Viper. This episodes marks a clear connection of friendship between Emily and Jordan, JJ's temporary replacement, with Emily vouching for Jordan to Hotch. There is also a scene where she and Hotch are in the locker room and they talk about dates, him scrutinizing her. Mention is made of the rough reception the team (specifically Hotch) gave Emily when she first appeared on the team. Episode 4x17 "Demonology" We learn Emily was living in Rome when she was 15. She got pregnant, possibly by John Cooley, and had an abortion. She was religious at the time. She speaks at least some Italian. She seems to be pushed away by Hotch in this episode but accepted by Rossi and we see one of her first really defining moments.
Season 5	Episode 5x1 "Nameless, Faceless" Emily is the one who realizes Hotch is missing and finds the bloody scene at his apartment; she alerts the team, then stays with him at the hospital. Later, she puts the pieces together to find the unsub who's been murdering ER doctors. Episode 5x11 "Retaliation" Emily and a local cop are escorting a prisoner who arranges his escape by having a partner drive his truck into their car. The car pitches down a ravine; Emily is left bleeding with a concussion and a heavy sense of guilt because she isn't able to stop the prisoner from strangling the cop and escaping. Still, she gets free of the car wreck by smashing through the windshield and climbing out. She flags down Morgan, who takes her to the hospital amid her protests. Later, he hypnotizes her so she can recall the accident, which is instrumental in finding and stopping the escapee and his surprisingly reluctant partner.
Season 6	Episodes 6x13-6x18 "The Thirteenth Step," "Sense Memory," "Today I Do," "Coda," "Valhalla," and "Lauren" Emily's past begins catching up with her. As a former nemesis named Ian Doyle tracks her down, we learn that she used to profile terrorists for the CIA, and her BAU colleagues are stunned when they uncover her real record. In 6x17, "Valhalla", she realizes that she'll have to confront Doyle alone to protect her friends at the BAU; in 6x18, "Lauren", Doyle captures and tortures her. At the climax of the episode, he impales her with a wooden stake and the team is led to believe that she has died on the operating table. By the end, we discover that Hotch and JJ have instead faked her death to save her from Doyle, who remains at large. The rest of the team is unaware she's alive; they attend her funeral and grieve for their loss.
Season 7	Episodes 7x1 "It Takes A Village" After seven months,Hotch and JJrevealedto the team that Emily is alive. We learn that Emily took care of Doyle's son and his housekeeper/caretaker in secrecy; she provided them a house and boarding school. After Doyle died, she accepted to be part of the BAU again.