"I bet you didn't expect to be talking about brain science here," Katherine said, hoping she succeeded in stimulating the brains of the seven people sitting in front of her instead of putting them to sleep. "But there are a lot of new findings that help us explain why people become criminals."

"Because they're psychos," muttered Miguel Nabarro, a serious-looking, muscular Latino whose oversized right bicep was adorned with a dagger. His Bronx-accented remark caused the rest of those present to chuckle and smile.

"Not all of them," Katherine improved on him. "But you're not entirely wrong either, Miguel. It's just a little more complicated."

Miguel and his five young colleagues, seated at a modern graphite-colored table in front of her, were BCU students.

Katherine turned to the plastic board behind her and wrote a single word: EPIGENETICS. She underlined it before turning back to the group. "Does anyone know what epigenetics is?" she asked.

Unsurprisingly, no hands were raised. And the only man in the room over forty, Professor Walt Bates, was smart enough to hold back.

Bates was a 'friend' of Katherine's mentor, Claire Galloway, and there was speculation the two were much more than that. He taught the course Katherine was currently in, an advanced seminar in profiling, and had asked Galloway if Katherine would feel comfortable serving as co-lecturer and educating his students about recent developments in psychiatry and genetics, particularly the increasingly important field of epigenetics and its possible application to criminal behavior. Galloway had approached Katherine about his request shortly after she returned to work two months ago. At the time, it had been the last thing she felt like doing. But she owed Galloway something for her sympathy, for her understanding and flexibility about Katherine's leave of absence, and felt unable to refuse. Thinking it was a one-time thing, Katherine decided to just get it over with, hoping it wouldn't cause her too much pain.

Fortunately, things turned out differently than she had expected or even feared. There were only six students in the course, plus Professor Bates, in a small but not at all claustrophobic seminar room. To her surprise, she had blossomed the moment she started talking as if she were telling a story to a gaggle of friends at a dinner party and had engaged the students in a lively conversation about her experience tracking a serial killer last year. They had listened raptly and asked numerous questions, Bates had been enthusiastic, and the way he and Katherine took turns leading the course had proven to them that they worked well together. Katherine, for her part, was shocked to find such pleasure in teaching and enjoyed the distraction regardless of any hesitation.

This was session number two. And judging by the expressions on the students' faces, it would not be such a success as last time. Epigenetics was a dry subject even for people with medical backgrounds, and the young people here were all on their way into law enforcement, whether as cops, FBI agents, or forensic investigators. Not that that branded them as less intelligent or high achievers. Miguel Nabarro, for instance, had somehow managed to be raised by parents who belonged to a gang without being killed or wounded and without getting a criminal record. A straight-A college student, Miguel planned to go to law school after graduation and then join the FBI. Despite his rough edges, Miguel was Katherine's hero. Against the odds he had had to overcome, medical school seemed like a cakewalk. Still, he and the others were laymen, and Katherine had better come up with something to make the subject interesting.

So she looked Miguel in the eye and started talking. "Epigenetics is the branch of study that looks at how genes keep changing over time without DNA changing as well, and what causes that evolution."

"You mean how animals adapt to changes in their environment," said Kara Maddox, a petite blonde from Plymouth who dreamed of joining the BPD, to the dismay of her wealthy family.

"How their genes adapt, and so do ours," Katherine replied. "And the environment doesn't just include the air we breathe, water, food -"

"And all the chemical crap in it," scoffed Wesley Phelps, a witty, smart, intellectual, and handsome dark-haired wannabe prosecutor with slate-gray eyes, or at least that's what his Facebook profile said. "You are what you eat."

"You'd better speak for yourself," said Justine Hu, an attractive twenty-four-year-old majoring in forensics. She had black hair, heavily made-up eyes, and her red lipstick was a shade above what Katherine still found tasteful.

Before Miguel could interject how Wesley's answer could possibly apply to Justine's sex life with the girlfriend she was living with, Katherine decided to make a preemptive strike. "That's true, Wes, but it's not the whole story. We're also defined by where we came from, where we lived, and with whom. How we were raised. Whether we were victims of trauma at some point in our lives, physically or emotionally. All of these factors create reactions in our bodies and in our brain chemistry that leave traces on our genes, chemical traces. So if you think of the DNA in these genes as computer hardware, the mechanisms of epigenetics are like software that directs or influences how the genes work overtime."

"When you say over time, do you mean our lifetime?" asked Leslie Carmichael, a pretty African American woman with long dreadlocks tied into a ponytail. Leslie had just returned to college at thirty to finish her degree after taking a six-year break to care for her chronically ill mother, who had recently died.

"Yes," Katherine said, "Although there is recent evidence that epigenetic changes to our genes can be passed on to future generations. One study followed a group of children who were born massively underweight because their mothers were pregnant during a famine. Sounds logical, right? But these children then grew up adequately nourished. Anyone wants to guess what happened when they gave birth to children of their own?"

Cory Mathis, a lanky twenty-five-year-old from Salem who still suffered from acne, raised his hand before Katherine finished speaking. "The babies were low birth weight, too," he said.

"Enough of them to show a trend, anyway," Katherine confirmed. "But let's go back to the beginning -"

"Slow down," Miguel interrupted, waving a hand. "Are you saying I was in a gang because my parents were in one, too, and my kids will be, too? Because I'll kill them if they do."

"But your kids are going to be born into a family where the parents have responsible jobs and grow up in a positive atmosphere," Katherine reminded him.

"First he has to find someone who will put up with him and make some kids with him," murmured Justine, who had a love-hate relationship with Miguel.

"You want to volunteer?" the latter returned with a mischievous grin.

Professor Bates had to stifle a laugh, but he knew it was time to intervene. "Maybe one of you clowns could consider why all this has anything to do with criminal behavior," he interjected, restoring calm and focus to the seminar. Katherine gave him a grateful look and reminded herself that teaching was more than just sharing knowledge. It was an exercise in reconciling the personal dynamics of very different people.

"Okay," she said after a deep breath. "Who has an idea?"

"It's kind of like Miguel said, right?" opined Kara. "That if you grow up in a family of criminals, you become one yourself by osmosis. Like Tony Soprano," she concluded, proud that the TV character had come to mind.

"That's a fictional character," Leslie said scornfully, with a tone that expressed 'What an idiot you are.'

But Katherine suddenly felt inspired by the post. "Wait, Leslie," she said, "There are many examples of this in pop culture. Let's stick with Kara's comparison. What else do we know about Tony Soprano's background?" She could almost see their brains working. Katherine herself didn't watch much TV, but her deceased boyfriend Nathan had been hooked on The Sopranos.

"Well, his father and brother were both mobsters, weren't they?" said Justine.

"And his mother was a crazy bitch," Miguel added.

Katherine's hand automatically went in Miguel's direction. "Tell us more about that," she encouraged him.

"She was cold, for example. She'd say something, and afterward, she'd claim she never said it. She disappointed Tony all the time. She called him a good son one moment, and the next she was yelling at him that he was a puto for not being as tough as his father. She even tried to have him beaten up." He said it without his typical pomposity, calmly, as if it were a fact.

To Katherine, it was like a glimpse of how Miguel could possibly overcome his parents' epigenetic legacy. "Miguel nailed it," she said. "What happens when a pregnant woman takes cocaine or heroin?"

"The child is born a junkie," replied Wesley, who had been mostly silent until now.

"Okay, so let's say you had a mother like Tony's," Katherine continued, seeing genuine interest and focus on her students' faces. "What do you think might happen?"

"I'd spend the rest of my life on a psychiatrist's couch if I didn't pop antidepressants," Wesley said levelly. "So would he."

"Or his son," Cory added, "who's turned into a real lunatic."

Katherine nodded. "Exactly, and science supports that statement. A study published in 2010 demonstrated a link of childhood abuse, sexual or physical, or even just in the verbal form Tony experienced at the hands of his mother, with the stunted activity of a gene that regulates the hormones we release under massive stress."

"So if your parents are yelling at you all the time, you don't stand a chance," Kara said.

"And they don't even have to do that. Another study in 2011 found that the children of parents who were under severe stress in their first three years of parenting had epigenetic traces on certain genes that were still there when the kids were fifteen."

"And by then, the child has probably gotten into trouble, and it's too late," Wesley opined, as Professor Bates unobtrusively pointed to his watch because time was up.

"Right," Katherine said. "And at this point, we'll call it a day."

The students flipped their laptops shut and thanked Katherine before heading off to their next classes.

"Excellent job, Kate," Bates said enthusiastically. "You really tied them up."

"Kara saved my ass, in a way," Katherine said thoughtfully. "I wish I'd come up with the Soprano story myself."

"Can I give you some advice?" asked Bates in a way that reminded Katherine of Maura.

"I'll take any advice you have," she replied.

"Don't stress about this," Bates said kindly, slipping into an ancient plaid jacket with lapels of a width that had long ago gone out of style. "When you start teaching, you start out thinking you have to know everything. But you don't really become a teacher until you discover the secret of learning more from your students than any book can teach you. Or them."

Katherine couldn't help but grin as she brushed a strand of hair from her face. Her former mentor had said something similar to her on his deathbed, that he had learned so much from her. She hadn't thought of it again until now. It made her feel closer to Bates and she was proud of herself as she left the room.

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Katherine rushed out of the Mass Gen elevator, hoping she would make it to her office before Galloway noticed her absence. But after only a few steps, a voice sounded behind her, as she had feared.

"Good morning, my dear." The sincerity that sounded from her reinforced Katherine's guilty conscience. Dr. Claire Galloway had been in charge of Mass Gen's psychiatry department for more than ten years, and in addition, had now inherited command of the research project in forensic psychiatry where Katherine was just beginning her second year as a fellow. Galloway was well-groomed, in her early sixties, with silver hair that she had recently stopped dying auburn. Today she wore a charcoal Armani costume and several rows of pearls. Her face was completely relaxed.

"Sorry I'm late," Katherine said, gasping for air.

"No problem," Galloway replied. "I just assumed you were still in the class. How did it go?"

"Better than I thought it would," Katherine replied. "The students seemed to like me. But you already know that."

"Guilty," Galloway said with a smile. The pair's relationship had gone beyond the usual chit-chat since Katherine started seeing her mentor once a week in therapy. She knew Galloway fairly well by now and had correctly assumed that Bates had already reported her progress. And Galloway knew that she knew. "So how are you getting along?"

Katherine was silent, wondering how to answer. "Fine. I'm doing fine," she replied.

"I think I saw Rosa Castillo waiting outside your door," Galloway said.

Katherine smiled and looked at her watch. "My model patient. Early as usual." But she hadn't even made rounds on her other inpatients. Galloway seemed to read her mind.

"I'll take care of your patients."

"Thank you," Katherine said, glad she didn't have to keep Rosa waiting.

"You're welcome, my dear," Galloway replied but made no move to walk away. Which signaled to Katherine that the conversation wasn't over yet.

"Is there anything else, Dr. Galloway?"

"I've had the impression lately that something's been bothering you. Is everything all right?"

Katherine took another deep breath and decided to tell the truth. "I'm having nightmares again."

"How does your schedule look today?" asked Galloway with concern.

"Full."

"Come by when you're free," Galloway suggested.

"Thank you," Katherine said. "I will."

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He maneuvered the car through Boston's heavy morning rush hour traffic. He had searched extensively for the right car for exactly the purpose he wanted to devote himself to today. Owning a car was insanely expensive in Boston, and finding a parking spot was a pain in the ass. And even though he was glad to be rid of it soon, the irony didn't escape him. Driving calmed him, especially here, because it was another way to create order out of chaos. So many vehicles jockeying for position, honking horns, and squealing tires, and in the end each one arrived at the right destination. Which in his case was just a few blocks away. He glanced at the clock on the dashboard and smiled. He would arrive on time after all.

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Rosa Castillo stood outside the door to Katherine's office. As Katherine approached, she saw that her pretty twenty-four-year-old patient, her dark brown hair hanging almost to her eyes, appeared deeply depressed.

"What's wrong, Rosa?" asked Katherine anxiously as she unlocked her office door. She noticed that Rosa was shaking as they entered together.

"Child Protective Services says I still can't see my babies," the young woman replied, flopping down on the comfortable dark green suede sofa. Along with the brown leather chair Katherine sat in, it was the only colorful item in an otherwise soberly functional office.

Nothing hung on the walls, not even Katherine's diplomas.

"Tell me everything, from the beginning," Katherine urged. She already knew most of it. Six months ago, Rosa had been doing really well. She had been cleaning office buildings at night and doing such an excellent job that she had caught the eye of Larry Merchant, the owner of the cleaning company, who had promoted her to shift supervisor in the office towers of one of his major clients. The higher pay that came with it allowed Rosa and her husband Franco, who worked for Boston's garbage collection service, to move with their two children, two girls around the ages of three and four, from their cramped two-bedroom apartment in Jamaica Plain to a clean four-bedroom apartment in Cambridge.

Life was treating her well. Until one night shortly after she began her new job, when she saw Larry Merchant walking toward her, smiling. He expressed satisfaction because everything was spick and span, then he pulled Rosa into the CEO's office and began groping her in no uncertain terms. When Rosa refused to satisfy him and pushed him away, Larry threatened not only to fire her but also to report her to ICE. Rosa, taking no shit, retorted that she was born in Lincoln Hospital in the Bronx and thus was as much an American as he was, and if she had to blow him to keep her job, he could stick it. Then she marched out the door. And straight to the nearest police station, where she filed charges against Larry Merchant for sexual assault.

When the cops arrested him the next morning, he told a very different story. He claimed that Rosa had come on to him, and when he rejected her advances, she had threatened to tell his wife that he was having an affair, and that was the only reason he had promoted her in the first place. In the world of law enforcement, this was the classic case of he said - she said in sexual assault cases. Rosa's word against Larry's. There were no witnesses. Rosa showed no evidence of an assault.

The Division of Sex Crimes detective who listened to Rosa's story presented the case to a district attorney, who concluded that the case was doomed from the start. She instructed the detective to release Larry.

Rosa was disgusted, she was only encouraged by the fact that at least the bastard couldn't fire her because she had already resigned of her own accord. She was convinced that she and Franco would be able to make ends meet with just his salary, at least for a while. But that was just the beginning of the difficulties.

A week later, Franco came home from work and announced that their marriage was over. He was leaving her for a woman with whom he had been having an affair for almost a year. When Rosa approached him about child support, he said she should have screwed her boss to keep her job, and if she wanted to see a dime from him, she would have to take him to court.

Rosa immediately went to a neighborhood exchange office she had used many times before and cashed two checks for five thousand dollars each. The owners were reluctant to pay her that much money, but they knew Rosa and liked her, and when she explained her situation, they felt sorry for her. And they had never liked Franco. So they gave her the money, which she used to pay three months' rent for her apartment.

Unfortunately, Franco had already drained their accounts. When Rosa's checks bounced, the owners of the exchange office called the police.

Rosa tearfully explained to the detective who arrested her that she had had no idea that her bank account was empty and that she was sorry.

The detective took pity on her and recommended that the district attorney's office not press charges because there was no intent and therefore no crime had been committed. There, however, they saw the case as an easy win and charged Rosa with two counts of fraud.

Suddenly Rosa, who had not had the slightest trouble with the law before, was facing seven years in prison. She was tried, found guilty, and sent to the Corrections Department. Her mother, Maria, promised to bring the children over as often as she could. She kept her word as long as she could, coming to visit with them at least once a week. But eventually, Maria had to go back to work six days a week to support herself and the children, and Rosa saw her little ones only twice a month. And then things got much worse.

Rosa was assigned to duty in the dining hall, where she helped prepare and serve meals to fellow prisoners. Although there were only female correctional officers in the female prisoners' cell wings, the supervisor over the dining hall and the women working there was a man named Jack Harding. Harding took a liking to the pretty, petite Rosa. One evening, not long after she began her duties in the dining hall, she was assigned to clean up after dinner. She was coming out of a cleaning closet with a broom when Harding pushed her backward back in, closed the door, and groped her. Rosa told him to stop. Harding responded with a blow to the head. He then pulled down her pants, forced her to bend over, and raped her. When he finished, he said if Rosa told anyone about their encounter, the next blow to the head would be fatal.

The women who found Rosa bleeding in the chamber warned her not to report the incident. She was not Harding's first victim, and the rest of them knew that the best way to deal with the man was to simply give him what he wanted. They assured Rosa her time in jail would go more smoothly if she did. Rosa nodded and said she understood.

The next day, she called her public defender, who in turn called SVU. Just a few hours later, the attorney showed up with a teddy bear from a detective named Mcneil and a court order to move Rosa into protective custody.

She was taken to Mass Gen, where she was examined and forensic evidence of the rape was collected. She then gave her statement to Detective Mcneil.

Mcneil told her he had an informant in the Corrections Department who knew exactly what was going on and corroborated Rosa's story. He would have Rosa placed in a hotel and under round-the-clock surveillance while the forensic lab ran the DNA test from the swab taken from her on an expedited basis. He had been trying to catch Jack Harding for years, but none of his victims had been willing to testify. Detective Mcneil asked Rosa if she would testify in court against this monster so he could never victimize a woman again.

Rosa said yes. And the events that followed almost made her dizzy.

Harding was arrested. A DNA sample was taken from him and compared to the DNA of the semen found in Rosa. There was a hundred percent match.

As word spread among the female inmates, more than a dozen of women came forward claiming they were like Rosa Harding's victims. And like Rosa, they were all first-time offenders who had not committed a violent crime and were serving a short sentence.

Harding was charged with forty-two counts of rape and sexual assault. The evidence against him was watertight.

The City of Boston contacted Dr. Galloway and inquired if her psychiatric fellows were available to evaluate Harding's victims to determine if they were eligible for early release and to provide care for them as they were unquestionably victims of sexual assault suffering from post-traumatic stress disorder.

Galloway agreed and assigned Katherine to Rosa Castillo because she trusted her to help Rosa come out of the trauma she had suffered.

Katherine determined not only that Rosa was a candidate for early release, but that she never belonged in prison in the first place. She and her colleagues in the program made a similar judgment with each of Harding's seventeen remaining victims, recommending their immediate release from the Corrections Department as well as a suspension of sentence to probation where deemed necessary.

Within a week, all of the women were released from prison on parole. None of them, however, had to testify against the corrections officer who assaulted them, because the night before the trial, Jack Harding sat down in a TV chair in his seventies-style wood-paneled living room with a 9mm Glock and blew his brains out.

Now Katherine was helping Rosa cope with the rape and put the wreckage of her life back together. Every conversation began and ended with the two things that mattered most to her, her children.

"The woman from juvenile services said as long as I'm on probation, I can't see them," Rosa recounted.

"That's absurd," Katherine retorted and meant it. "You've never done anything to the kids. You love them. I'll talk to her and see if I can work something out with her."

Rosa calmed down a little. "I thought it would be great to get out of prison," she said, "but now I'm scared."

"What are you scared of?" asked Katherine with a slight frown.

"That I won't be able to be a good mother to them. That I'll always be the mother who was in prison."

It pained Katherine to see this young woman, who through no fault of her own had already been through so much, plunge into such self-doubt. "Rosa," she said, "you are a fighter." That's as far as she got before the tears started streaming from Rosa's eyes. Katherine handed her a tissue and continued, "All your children need to know is that you are their mother. You love them. And believe me, your children know that now because everything you did, you did for them."

Rosa nodded and wiped her eyes, but she wasn't convinced. "It's just ... You think life is going your way, and then all of a sudden something bad happens. And after that, you're not free anymore because you're always waiting for the next bad thing to happen, you know?"

Yes, thought Katherine, I know that better than you could ever imagine. Aloud she said, "I understand exactly what you mean. But life is a journey. I'm here to help you. If you continue to be the model patient you've been, there's no reason why your life shouldn't go back to the way it was."

"With everything?" asked Rosa.

Katherine smiled. "And a little something to go with it," she said encouragingly. "How is it, do you still have nightmares?"

"Less and less," the other woman replied. She described them, a man chasing her and always almost catching up, but Katherine's mind wandered. She reflected that she was a kindred spirit of Rosa's, that her life and that of this little-educated but nonetheless confident young woman ran parallel.

Why can't I be at peace with myself? Why don't I feel free to live my life? What's holding me back?

"Dr. Isles?" asked Rosa. "Are you all right?"

Katherine struggled to regain her composure. In the past, she would have tried to play it off. But she had realized that honesty with her patients was best. "I'm sorry, Rosa. I must have been daydreaming a little," she apologized, standing up and extending her hand. "Come on, I'll walk you to the entrance hall."

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He parked the car on the side of the road and a loading zone and placed the plastic card on the dashboard so that he wouldn't get a ticket or be towed. This card, the equipment he had placed between the two front seats, just like the make and model of the nondescript sedan itself, would guarantee that this car he had been looking for for a long time would still be there when he returned.

Then he walked quickly, but without attracting attention, around the corner, to a spot across the street from the huge building. He looked like any other of the thousands of suit-wearing businessmen hurrying through the chaos. Even though he knew he was different from everyone else and proud of it, today he was content to just blend in with them. He knew he had arrived on time. He would only have a few minutes to wait.

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Katherine and Rosa walked silently through the entrance hall. Rosa's serious expression made Katherine feel she had offended her patient because her mind had wandered during the session. Deciding to tackle the problem head-on, she stopped and turned to the young woman. "Rosa, what I did up there was unforgivable. It shouldn't have happened that my mind was somewhere else. I promise it won't happen again."

Now Rosa seemed even more uncomfortable. "Doctor, I don't want to interfere in other people's business. But please don't say you're sorry. You've helped me so much -" She broke off, undecided how to finish the sentence.

"You really are amazing, Rosa," Katherine said. "And thank you for asking, but I'll be fine."

"I'll see you Thursday?" asked Rosa hesitantly, as if expecting the therapist to say no.

"Of course," Katherine replied. "Call me if you need anything."

Rosa left the building while Katherine turned around and hurried to the elevator. She always ended up needing a little extra time for her session with Rosa. She had another thirty minutes until her next appointment and hoped to check on her inpatients in that short time.

She rushed into an open elevator and looked at herself in the mirror. Damn, I forgot my stethoscope.

She pressed the button for the second floor. When the door opened, she ran to her office, retrieved the stethoscope, and slipped on the flat shoes she always wore on rounds since she had once slipped in a patient's bodily fluids in her high heels. She was about to run out of the room again when a flash of lightning alerted her to the spring thunderstorm brewing outside.

She looked out the window, from where she had a sweeping view across the street. Down the street, something caught her eye, and her worst fears seemed to come true.

A man in a dark suit was leading Rosa down the sidewalk. In handcuffs.

"No!" exclaimed Katherine, rushing out the door. She ran down the two flights of stairs, stormed through the entrance hall, and ran out into the street. There she looked in the direction the man in the suit had led Rosa away. But all she saw was the already viscous traffic come to a full stop and a sea of black umbrellas open almost simultaneously as it finally began to pour.

Rosa and the man were gone.

A few raindrops landed on Katherine's face, and she retreated into the hospital entrance. A chill ran over her that had nothing to do with the weather, but with the fact that this was a frighteningly familiar moment in her life.