A female police detective in 2016 discovers she is able to speak via a ham radio with her father (also a detective) who died in 1996. They forge a new relationship while working together on an unresolved murder case, but unintended consequences of the ‘butterfly effect’ wreak havoc in the present day.
When Detective Raimy Sullivan discovers that she can communicate with her deceased father on an old ham radio, she warns him of events that will lead to his death so he can circumvent his fate.
Raimy tells Frank, over the ham radio, that her mom will be murdered unless he can find a way to warn her; Frank gets bad news about Stan Moreno; Raimy follows a lead in the Nightingale case, while Frank and Satch follow the same lead in 1996.
When Raimy uncovers evidence in the Thomas Goff case, she relays this information to Frank over the ham radio, which prompts him to take matters into his own hands while ignoring a strong warning from Satch. Meanwhile, Gordo talks Raimy into going out for a drink where she has an interesting encounter with Daniel who still considers her a complete stranger and possible stalker. Lastly, Raimy struggles to adapt to life without Julie, and Frank tries to adapt to life with her.
With the date of Julie’s abduction rapidly approaching, Raimy and Frank each work to gather information from a girl whose mother was taken by the Nightingale. Meanwhile, Raimy meets Kyle who immediately remembers her from a brief encounter in the past. She doesn’t recognize him at first, but flashes of their night together come rushing back to her.
When Frank helps Raimy uncover clues from the past to help solve a present day murder case, it brings up two different memories of her first day in the NYPD. Through Frank, Raimy continues to learn more about Stan which begins to cause friction with Satch. Meanwhile, Frank has trouble controlling his jealousy as he struggles to give Julie her space.
In 2016, Raimy meets a strange character named Karl, who speaks to himself in the future. In 1996, Frank feels like he's being taunted by the Nightingale. Meanwhile, having discovered new information, Raimy and Frank set up a plan to use the Nightingale's next victim as bait.
Raimy and Satch’s detective work begins to pay off when a cold case victim leads them to their biggest break; a room where the Nightingale held his first victim.
Raimy and Satch discover a shocking connection to the Nightingale’s first kill. When Raimy shares this news with Frank, he works to dig up additional information. Meanwhile, Frank and Julie are forced to have an honest conversation, and Raimy has a surprise visitor.
Raimy and Frank make a startling discovery about the Nightingale killer. Meanwhile, Frank is blindsided by a shocking betrayal.
Frank and Raimy put a plan in motion for Frank to kill the Nightingale. Frank finds himself agonizing over whether it's the right thing to do, and Raimy is confronted with an unexpected moral decision.
Raimy and Frank find themselves in the thick of things. Meanwhile, Frank learns the meaning behind a betrayal.
Raimy and Frank make a huge discovery while continuing their search for the Nightingale. Meanwhile, Stan is willing to do anything to bring Frank down.