After fighting with her brother Nick Brewer at a family dinner, Pia Brewer angrily goes drinking and accidentally drops her phone in the toilet. The next day while at work, a patient shows her a video of Nick visibly beaten and holding up a card that says "I abuse women." He then holds up a different card that says "At 5 million views I die."

Distraught, Pia attempts to contact Nick but has to call from her work phone since her phone is still drying. When Nick doesn't answer, Pia goes to his work place, but learns that Nick is not there. Pia then goes to Nick's wife Sophie at the school where she teaches. They proceed to go to the police where they meet with Detective Roshan. He assures them that everything is being done to verify the video.

Nick and Sophie's kids, Ethan and Kai, have also seen the video and are staying out of school. Pia retrieves her phone and finds a voice message from Nick who apologizes for their fight and says there are things he needs to talk about with her. Pia asks their mother if she has heard from him, but after realizing she has not, opts to keep her in the dark about the video instead. The police ask Sophie and Pia to return for a secondary interview after a second video is released: Nick holding a sign that reads "I killed a woman." Sophie and Pia confirm that while the first two signs were in Nick's handwriting, the third one is not. The investigation now moves from a missing persons case to homicide.

It is confirmed that Nick was held in the abandoned van where he was forced to film the videos. Senior Detective DeLuca from homicide is now in charge, and he takes Detective Roshan Amiri off the case. DeLuca seizes all mobile devices from the Brewer family to look for clues, but Pia claims that her phone is still drying at home.

Wanting to be back on the case, Detective Roshan makes a deal with Pia that if she requests his continuous involvement in the case as a liaison, he will keep her in the loop about any progress in the investigation. Roshan discovers Ethan still has a tablet that Nick owned, where he is monitoring Geonicking, an app where volunteers mark on a map where they have searched for Nick (albeit for voyeuristic reasons). Roshan shows his sergeant the application as well as a journal entry on Ethan's phone about Nick and Sophie fighting.

Roshan also hands the tablet to DeLuca, telling him they "missed it" after DeLuca continues to minimize Roshan's involvement. Under police advisement, Sophie releases a statement that the kidnapper is mistaken and that Nick has not committed any of the crimes he is accused of. Pia hands Detective Roshan her phone with the voice-mail, which Roshan shows to his Sergeant. He also admits that prior to Nick's disappearance, he was about to meet with Pia through a dating app.

Upon leaving his sergeant's office, he finds that DeLuca has placed photos from his dating profile around the office in an attempt to ridicule him. Roshan confronts DeLuca, claiming him to be a racist who is minimizing Roshan's involvement because Roshan is a Muslim. DeLuca retorts that his issue with Roshan is with Roshan's inability to work with others, and that his interest in the case is to receive a transfer to homicide.

The police manage to locate where Nick appeared to have been abducted, locating a syringe nearby. Roshan shares this information with the Brewer family, and confronts Sophie and Pia separately on any issues with Nick. While Sophie vehemently denies having any marital issues with Nick, Pia admits that a few months prior Nick came to her to be treated for bruises, asking her to keep this between them. Following a lead from the Geonicking app, Roshan and Pia rush to the docks where a body appears to have been found. They quickly realize it is a mannequin with Nick's face taped to it as a joke.

Detectives Roshan and DeLuca break the news of Nick's death to Sophie and ask if she can identify the man in the surveillance footage. She denies knowing the man, until Roshan shows an image of him wearing the same shirt in a photo with her on social media. Sophie says the man is Curtis Hamilton, a former colleague she insists is just a friend.

Sophie returns home to break the news of Nick's death to her children and Nick's mother. Pia asks Roshan to show her Nick's body but is turned away as his body is still being examined by the coroner. Sophie tells her mother about the fight Curtis and Nick had, and her decision not to disclose the affair to police.

Sophie sneaks out of the house that night to meet with Curtis and ask about his involvement with Nick's disappearance. DeLuca and Roshan arrive in the middle of their conversation and arrest Curtis after he refuses to cooperate by surrendering his digital devices. While at the police station, Sophie discloses her affair with Curtis, and that when Nick found out he was initially upset, but made up with her afterwards.

The next day, Ethan and Kai find footage of Curtis's arrest and question why Curtis would have wanted to hurt Nick. Suspicious, Pia confronts Sophie, who admits her affair; they are overheard by Ethan and Kai. Upset, Ethan leaves the house and Sophie tries to follow him.

While visiting various skating parks, Sophie recognizes a woman who has been following her and confronts her. The woman introduces herself as Emma Beesly. Emma tells Sophie that she was in a relationship with Nick, who used the pseudonym "Danny Walters." While initially skeptical, Sophie starts to believe Emma after she mentions that their relationship began six months ago: when Sophie told Nick about her affair. Emma also explains that she lives in LA, where Nick frequently traveled for work.

Sophie finds Ethan at Pia's apartment and discusses with Pia how they could verify Emma's story. They attempt to access the profile of "Danny Walters," but find that it has been deleted. Pia asks Vince to help retrieve the profile from the dating site.

Later that day a memorial is being held at Nick's workplace and information regarding her affair with Curtis has leaked to the press. Roshan and DeLuca inform Sophie that Curtis has been released after establishing an alibi. Before the memorial, Jenny, a student who worked with Nick, attempts to tell Sophie something about Nick, only to be cut off by Nick's coworker Matt. Vince arrives at the memorial and shows Pia the profile of "Danny Walters" is Nick.

Emma Beesly gives her statement to the police, disclosing her affair with Nick. Emma's daily life as a successful insurance agent is shown along with her relationship with Nick under the name "Danny." On the day Nick is kidnapped, she was at the gym with her friend Audrey, learning of his situation via the news.

Emma follows the case closely, and decides to go to Oakland to help shed more light on the situation. Emma waits outside the Brewer house, hoping to find an opportunity to talk to Sophie. While waiting, she gains the attention of a reporter, Ben Park, who gives her his card. At this moment, Ethan storms out of the house after finding out about Sophie's affair (shown in the previous episode), followed by Sophie whom Emma follows.

Emma tries to work up the courage to talk to Sophie, who confronts her after noticing that Emma is following her. Emma tells Sophie about her affair with Nick and returns to her hotel room. Audrey calls her and asks why she went to Oakland. Emma admits she wanted to see Nick's life in Oakland. The next day, Emma goes to give her statement to Detective Roshan. Not wanting to return yet, Emma goes to Nick's workplace to see his shrine and meets Matt. Pia then arrives to ask Matt if he was aware about Nick's affair, learning about Emma's arrival earlier.

Meanwhile, Sophie begins to receive death threats on her phone after someone put her phone number online. Pia confronts Emma at her hotel room, telling her that she has no place being there. Emma insists that what she and Nick had was real, and shares details that Nick told her about his childhood with Pia.

Emma receives a threatening phone call telling her to leave town. She calls the police and leaves the hotel followed by a green truck that runs her off the road. At the hospital, Emma gives her statement to Roshan. Pia arrives as well (having been contacted by Emma) and learns that Nick had multiple online personas where he met different women.

Ben Park shows the interview he had with Emma to his editor, Dakota. His editor orders him to find more information on the matter and get an interview with Sophie. Ben poses as a food delivery man, and films the inside of the Brewer home when he is discovered by Pia. Ben leaves his card with the Brewers before being chased out of the house.

Returning home, Ben and his boyfriend Cameron attempt to find Nick's online dating profiles, and discover Jenny commenting on an online forum that anyone who attempts to defend Nick did not really know him. Ben interviews Jenny the next day at the college, who tells him she believes that Tara Wilson, a girl on the volleyball team, may have left due to abuse from Nick.

Sophie brings her lawyer to meet Ben's editor, Dakota, to sue the network for Ben's trespassing. Dakota offers not to air the interview with Emma Beesly if Sophie will do an exclusive interview with them, to which Sophie agrees. Dakota removes Ben from the story, much to his chagrin.

Undeterred, Ben continues to search for Nick's dating profiles and finds a persona he used: Jeremy Wilkerson. Through the dark web, Ben obtains access to the dating profile, and discovers that Nick was involved with a woman named "Maggie Oxley." Using photos from her dating profile, he tracks her location to a bookstore in Sacramento. While there, Ben and Cameron learn that "Maggie Oxley" was an alias for Sarah Burton who died four months ago.

They learn that she has an older brother, Simon, and go to his apartment. Ben breaks in and finds Sarah's phone, narrowly managing to escape Simon when he returns to the apartment. Upon returning to Oakland, Cameron is upset at Ben's callousness and insensitivity and decides to spend the night at his parents' house. Ben goes through Sarah's phone and discovers that Nick was ignoring her, eventually goading her to commit suicide after she threatened to do so.

Six months ago, Simon Burton worked as a content moderator for Klonis. Through spyware he installed on his sister's laptop, Simon learned that she had begun a relationship with someone named Jeremy. While initially skeptical, he was overjoyed that this new relationship helped her get her life on track. As time passed, Sarah's relationship with "Jeremy" worsened, and she began to spiral out of control. Four months before the events of the first episode, Simon received a call from Sarah moments before her suicide. As the coroner removed her body, Simon discovered how "Jeremy" goaded her into suicide. With the help of his friend Darryl, Simon uncovered "Jeremy" as Nick Brewer.

In the present, Darryl and Simon are upset that the police are at their workplace. As Roshan questions him, Simon feigns ignorance and claims that he was fishing with Darryl when Nick was kidnapped. As Roshan leaves, Simon messages Darryl to lay low and not be found. Later that day, the two of them meet to corroborate their alibis.

Meanwhile, Sophie has decided to remove all of Nick's pictures from the Brewer house, causing Pia to be upset and leave. She learns from Roshan that Simon is now a suspect, and they drive to Sacramento to meet him. The two discuss their suspicion that the only picture Simon has posted of himself was for the day that Nick was kidnapped. Roshan and Pia almost sleep together, before Roshan refuses as doing so would have him removed from the case.

The next day, Roshan asks Simon to follow him to the Sacramento police department for an interview, but Simon runs instead, only to end up arrested anyway. While at Simon's workplace, Pia spots a nervous and anxious Darryl, who recognizes her as Nick's sister. Darryl attempts to hold her at gunpoint, but Pia escapes and asks a bystander to call police. As Simon and Darryl are arrested, Simon reflects how the two of them went to Oakland to kidnap Nick and force him to hold the cards for the videos.

Simon tells Roshan that he will only give a statement if he can first talk to Pia, who agrees. After telling Simon that Nick's death accomplishes nothing, with Sarah still dead, Pia learns that Simon did not kill Nick. Instead, Simon reveals that when he confronted Nick on his treatment of Sarah, Nick denied ever knowing her and insisted that he never made any dating profiles.

After Simon and Darryl are arrested Ethan and Kai return to school. While Kai's friends are happy to see him again, Ethan's friends attempt to maintain distance. School bully Michael unsuccessfully attempts to goad Ethan into a fight, but Kai overhears and punches Michael instead, beginning a brawl.

Sophie is asked by the school principal to come by to talk about Kai's behavior, and learns the next day that Michael's father intends to pursue charges against Kai. Sophie convinces the school principal to set up a mediation between the two families.

At dinner, Pia shares her belief that Simon did not kill Nick, and that Nick was innocent after all. In a private conversation, Pia reveals to Sophie that their father had committed suicide when they were young, something which affected the family profoundly and why Nick would never have goaded Sarah into suicide.

Throughout the series, Ethan has been messaging Alison, a girl he met online. After watching an interview from Mandy Harrison, Ethan begins to suspect that she never met Nick in person, something that Mandy confirms with him via email. Ethan brings this information to Pia, who brings it to Roshan, but the police insist that Nick's case is closed.

While Sophie and Kai go to the mediation meeting with Michael and his father, Ethan demands to meet Alison in real life, suspecting that she is involved with Nick's murder and catfish. Alison insists that she cannot meet him as she has an anxiety disorder, but gives him her address to see her himself. Ethan goes to the address and finds that Alison was telling him the truth and apologizes. After an awkward start, the two begin to bond. Alison suggests that Ethan try to contact Emma Beesly, to verify if she has met Nick in person.

When Ethan asks Emma if she recognizes Nick's voice from an old video, she is unable to and admits she never met Nick in person. Alison tells Ethan that if he has the pictures the catfish sent Emma she could use the metadata to track where the pictures were sent from.

Pia meets with Vince and they deduce that since the catfish knew details about their lives it has to be someone that Nick knew well. Vince reveals that before Simon was arrested there were rumors that Nick was involved with Tara Wilson. Pia asks Tara if she had a relationship with Nick but she insists that they did not: Nick encouraged her to stop her relationship with someone else and not quit the team after learning the guy Tara was seeing began harassing her and eventually posted naked pictures of her online. As Pia presses further, Tara reveals that she was seeing Matt.

Ethan realizes that Kai was on his computer and saw the location that Alison sent. Kai knocks on the door of the catfish and Dawn answers. Kai believes that the location he found was an elaborate prank by Ethan and accepts Dawn and her husband Ed's invitation to come in before they drive him home. After learning how Kai found them, the two leave him in the dining room and Ed retrieves a gun.

Two years ago, when Nick first began working at the college, he asked Dawn for help setting up his computer. During this process, she learned all of his usernames and passwords. That same night, Dawn discovers a dating profile Nick made and abandoned when he was angry at Sophie, and she begins to impersonate him. She begins to set up multiple profiles using Nick's photos and is discovered by Ed who storms out. Sarah Burton repeatedly messages to ask why she is being ignored. Annoyed, Dawn goads her into committing suicide after Sarah threatened to do so.

In the present, Ed and Dawn pretend to drive Kai home as Sophie and Pia arrive at the now empty house and learn that Dawn was the catfish. Realizing something is amiss, Kai attempts to contact his family, only for Dawn to throw his phone out of the car. They bring him to a ranch nearby and keep him inside a trailer. There, Kai learns that after Simon released Nick, he came to confront Dawn about using Nick's pictures to catfish women and drive Sarah to suicide. While Dawn attempts to deny doing so, Nick points out that Dawn is the only person he had told about Sophie's affair and she had access to his computer. Nick attempts to bring Dawn to police, but Ed kills him. Kai escapes the trailer but is almost shot by Ed. Ed and Dawn chase him and he attempts to hide in a stable. Roshan and other police arrive and search the ranch. Hearing Sophie call out for him, Kai comes out of hiding but runs into Ed. Roshan and the police find Dawn and arrest her, while Ed holds Kai at gunpoint. Dawn convinces Ed to let Kai go, but Ed refuses to be arrested and forces police to shoot him.