Carlos and Kiera investigate the deadly handiwork of the mysterious serial killer known in 2077 as the "Ouroboros" Killer. Kiera knows that in the future, the case remained unsolved after a string of gruesome murders with few leads. In 2013, she's shocked to learn it's Carlos's case. She's now at a crossroads in history to help solve a crime that still wouldn't be solved sixty-five years in the future.
Carlos and Kiera meet with the daughter of the latest victim, a renowned musician. As Kiera probes his daughter Patsy about a history of sexual abuse, Carlos doesn't understand her obsessive focus on a seemingly wild hunch. Unbeknownst to him, Kiera knows the murder victims were all child molesters, a fact that hadn't yet been discovered in the investigation so far.
Meanwhile, Alec explores his relationship with his new girlfriend, Emily. After an awkward date, he invites her to dinner back at his lab.
At the precinct, Kiera is mocked by fellow detectives for her hunches based on her future knowledge of the case. She struggles with how to justify her theories while trying to nudge Carlos in the right direction without blowing her cover. Kiera visits Patsy on her own, interrogating her further about any sexual abuse. Horrified by the allegation but clearly covering up much darker secrets, Patsy refuses to cooperate.
Kiera receives a message from recently ousted Inspector Dillon. After weeks of silence, he wants to meet privately. When they do, they exchange a few remarks but Dillon offers little more information about what he's up to. Finally, after months of silence and mystery, Kiera meets with the ever-elusive Mr. Escher. He offers to be an ally, sharing common interests – and enemies. Kiera remains distant, calling him out as a "freelance" time traveler. Escher offers her the chance to connect with someone who truly understands her unique identity and place in time.
Carlos remains wary of Kiera's "crazy" theories. When they revisit Patsy to follow up on another one of Kiera's hunches, she realizes Patsy is the next victim. She witnesses a suspicious man packing a large case into his truck. Her CMR reveals a faint heat signature in the case; she instantly knows it's Patsy's body. Kiera stops the driver and finds Patsy barely alive in the case.
After Carlos interrogates the killer, he confronts Kiera on her almost spooky knowledge of intricate details about the case, even wondering aloud if she's in on it with the killer himself. Kiera denies any connection but still can't explain fully just how she knows what she knows.
Back at Alec's lab, Emily meets him for a romantic dinner where things heat up in the kitchen.
At the precinct, Inspector Harris reveals their apprehended killer has stage IV cancer and will most likely die before sentencing. Kiera knows about more victims and offers up a second killer theory. Outraged, Carlos dismisses her wild notion, forcing her hand. She reveals she is a time traveler from the future. At his wit's end with her, he storms out of the room, doubtful and alarmed by her confession.
In desperation, Kiera follows her lead to the home of the second killer. He flees and she follows him into the basement where he overpowers her. He intends to kill her for interfering in his vigilante killing spree. Before he can take a scalpel to Kiera, he sees the CMR microchip reflected in her eyes. She confides she's a time traveler and offers proof, guiding him towards her service weapon. When he picks it up and tries to shoot her, it kills him instantly.
Kellog, kicking Emily out of the lab, rudely interrupts Alec's date. Alec is apologetic and Emily understanding – or so it seems. When she leaves the lab and is out of earshot of Alec, she places a cryptic phone call to an unknown party saying, "I'm in."
Acting on information provided by Betty, Carlos finds Kiera alive but deeply shaken in the basement of the killer's house. He sees her service weapon reset itself on the floor. Sobbing , she begs Carlos to believe her as she grapples with the possibility she nearly died and thus would have never even existed in 2077. With little other explanation for so many strange coincidences with this case and other elements of her story, he invites her to tell him everything.
She begins, "My name is Kiera Cameron and I came here from the year 2077," as Carlos listens intently to her every word.