Before Season 1
Sarah Emerson and Adam Baylin began dating sometime before 1982, and frequented JP's Diner. Adam etched their initials into a table during their last trip to the diner. The appearance of Jessi as identical to Sarah, and of Kyle as identical to Adam, makes the old man still working in the diner think that "the lovebirds have returned."
When Sarah Emerson attended the University of Washington, she won many academic awards, and once got in trouble for painting the answers to a biochemistry exam in a lecture hall, along with the Latnok symbol. She also set a record for shooting pool still standing since 1984. She mysteriously disappeared after that, and was assumed to have died. Adam tells Kyle that Sarah fell apart from the strain of trying to excel in everything, and he could not help her. Adam feels guilty of abandoning her. It becomes a cause for Kyle to not do the same to Jessi.
Brian Taylor tells Kyle that he took the photo of Adam and Sarah. At some time and in ways not made clear, he arranged an embryo to make another experiment in prolonged artificial gestation and development at Zzyzx, code-named as 781228, which becomes Jessi. He says that he used genetic material from Sarah after she died; but that is not plausible, and we know that he is an expert and compulsive liar. He was able to provide genetic material to establish himself legally as the parent of Jessi; but we see that manipulated in Kyle's case. Brian is able to describe Sarah's personality as if he had known her very well; and she knows him well enough to predict his involvement with Jessi. Combined with Sarah's later complaints about Latnok running her life, we can imagine that Brian got Sarah pregnant, and 781228 was for her an alternative abortion that for her went bad. That would explain her disappeance, and her statement to Kyle that she "cannot be anyone's mother."
At the same time that Jessi is being overstressed by Brian, Kyle begins getting mysterious messages urging him to help Jessi. He immediately suspects they are from Sarah, and finally figures out that the messages are also arranging a meeting at the old diner. He sees a woman sitting in a booth, and she is wearing the Latnok ring Adam had told him about. He introduces himself, and she says she is Sarah.
Somehow, Sarah knows what Brian is doing with Jessi and why, and knows that he will push her too hard. Sarah also knows that Jessi will not be able to stop herself and will be badly hurt. Sarah is not fond of Latnok, believing that because they are scientists, they do not include human feelings and needs. She says that getting away from Latnok was part of why she had left and lived her own life. Sarah wants to help Jessi, but she leaves the restaurant without a way to get in touch with her.
Kyle finds her motel and exlains that Jessi will see what Brian is doing to her only if Sarah herself warns her. Kyle reminds her that she is Jessi's mother. Sarah says "I'm not her mother! No, I can't be anyone's mother." He reminds Sarah that she has been concerned enough to go to so much trouble already. He tries to arrange a meeting between them at the Trager house (Sarah says she knows where it is) on the same day Brian was going to display Jessi to Latnok. Only on the promise of finally meeting her mother does Jessi agree. But after she has waited "three hours and fourty-two minutes," Sarah has not come and Jessi walks away.
Kyle goes to the diner, and Jessi is sitting in the same booth. When Jessi accepts that her mother lied to her about coming, she goes into an agony of loneliness. Sarah arrives to announce "Jessi, you are not alone," but Jessi tells them it's too late. Sarah says "It never is." But she is wrong: with a double nose-bleed from the effort, Jessi has stopped her own heart in despondent suicide.
Sarah can only stand and watch as Kyle tries to save Jessi. His energy surge does revive her heart, while blowing out the lights. As he collapses in exhaustion, Sarah kneels at Jessi to tell her "It's okay now. I'm here." As Jessi's eyes flutter open and clear, she has a close view of her mother, whose hand is stroking her hair.
Sarah and Jessi take a walk together, and Jessi asks "Why didn't you come to the house?" Sarah says "I was scared." Jessi asks "Of me?" Sarah says "Of not being everything you want me to be." Jessi says "I just want to know you." Sarah says "I want to know you too." Jessi asks about Brian, and Sarah assures her "Kyle says he's taken care of it." With that, they have a nice walk and talk.
They go to Brian's vacant apartment for Jessi to pack. Sarah says she can buy all new clothes, make a new beginning. Sarah tells her that "Seattle was a trap for me for twenty years," and she wants to leave again. To please Sarah, Jessi agrees.
Jessi is putting her one bag in the car trunk, when she is stricken with worry about Kyle. Sarah says "You're just anxious about leaving. I know this is hard and scary, but you'll feel better once we get on the road. We have to get away from all this, we have to start our new life. Please get in the car." Jessi feels she must go help Kyle, and says no. As Jessi is running off, she turns to say "I'll be back."
Jessi will be back. But that is the last that Jessi, and the story, will see of Sarah.