In Episode 3 of Doubt, tension escalates as Detectives Jung-hwan and Yong-soo arrive to interrogate Ha-bin. Though Tae-soo refuses to open the door, Jung-hwan grows suspicious after noticing Tae-soo’s car outside. Ha-bin surprises everyone by opening the door herself, much to Tae-soo’s dismay. During the interrogation, Ha-bin shares her version of the events, claiming Min-ah stole her phone and that she was in a hotel room with her boyfriend for two days, including the day of Min-ah’s murder.
Detective Jung-hwan, however, remains skeptical. After the interrogation, he expresses his doubts to Yong-soo and notes that Tae-soo seems unsettled. Inside their home, Tae-soo confronts Ha-bin about her lies, and she lashes out, accusing him of always blaming her for accidents and deaths.
Later that night, Tae-soo discovers an identical red keychain in Ha-bin’s bag. Meanwhile, Ha-bin searches the internet for articles about her father, further fueling suspicion.
The following morning, the detectives question Ha-bin’s boyfriend, Soo-hyun, who confirms her alibi. Tae-soo also questions Soo-hyun later, asking if he knew Min-ah, but Soo-hyun denies any connection. He even urges Tae-soo to leave Ha-bin alone, insisting she’s a good person. At the police station, Eo-jin starts growing suspicious of Ha-bin after reviewing the incident report, but Dae-hong conceals the fact that Ha-bin is Tae-soo’s daughter.
At school, Tae-soo meets Ha-bin’s teacher, Joo-heon, who reveals that Ha-bin has been close to Soo-hyun for years. She used to make crochet keychains, showing Tae-soo one of them. Both the detectives and Tae-soo search for CCTV footage from the hotel where Ha-bin stayed. Jung-hwan confronts Tae-soo about being too involved in the case, suggesting he’s trying to protect Ha-bin.
Meanwhile, Ha-bin tells Soo-hyun that Tae-soo asked if he knew Young-min. She jokes that having a cop for a father makes her a better liar. As the episode progresses, the detectives gather their findings with Seok-moon, confirming the alibis of individuals near the murder scene. Jung-hwan, however, conceals that Ha-bin is Tae-soo’s daughter, preventing Eo-jin from exposing the truth.
In another subplot, the detectives argue with Dae-hong over Ji-yeon’s statement. Jung-hwan tasks Dae-hong with bringing in the other runaway kids associated with Min-ah, Young-min, and Ji-yeon. As the detectives prepare to arrest Young-min, Yong-soo questions Jung-hwan’s loyalty to Tae-soo. Jung-hwan explains that while he dislikes Tae-soo, he trusts that Tae-soo wouldn’t tamper with evidence for personal gain. Soon after, they spot Young-min’s neighbor, Sung-hee, who raises questions due to her young age and middle-school-aged son, Do-yoon.
Elsewhere, Ha-bin tries to open a locker at a safety deposit box but struggles with the pin. By the episode’s end, she successfully unlocks it. During dinner, she has an emotional talk with her father, suggesting that she’s willing to move with him if he transfers. She mentions how living in the house reminds her of her late mother, causing her distress.
The next day, Jung-hwan and the police arrest a group of runaway teens linked to Young-min. Tae-soo advises that they be interrogated individually to find weak links, staying out of the investigation due to his personal ties. The profiling team interviews the teens and discovers their negative views on Min-ah. They also notice that the teens’ stories about Young-min’s alibi seem rehearsed.
Dae-hong questions Eun-jin, who seems particularly nervous, and through empathy, she reveals that Young-min was not home as he claimed. The police then search Sung-hee’s home, where Young-min is hiding. Sung-hee begs Young-min to cooperate, but he becomes violent, attempting to strangle her. Her son Do-yoon intervenes, but Young-min escapes.
Tae-soo later reveals to the team that the crime was likely committed by two people, noting that the body was dismembered and buried simultaneously. After this revelation, Tae-soo hints that he’s considering a transfer.
Outside the station, Tae-soo receives a call from a man whose car was parked near the hotel where Ha-bin stayed with Soo-hyun. Dashcam footage shows Ha-bin leaving the hotel room on the night of Min-ah’s murder. This revelation devastates Tae-soo, who shares the footage with Soo-hyun. The boyfriend confirms that Ha-bin left the room but admits he doesn’t know her well, having only recently transferred to the school.
Tae-soo later learns from Ha-bin’s teacher that the Soo-hyun he spoke of was actually a female student who had dropped out of school. Soo-hyun’s father reveals that his daughter frequently ran into trouble because of Ha-bin.
Meanwhile, Ha-bin’s boyfriend gives her a new keychain, different from her usual ones. At home, Tae-soo confronts Ha-bin about the keychain, stating that he won’t stop searching for the real killer. Ha-bin retreats to her room.
Elsewhere, Young-min locates Ji-yeon in a hotel room and assaults her for attempting to flee. He scours various lockers for a bag of money, unaware that Ha-bin has already taken it. The bag is filled with cash.
The next morning, Ha-bin asks Tae-soo to drop her at the library, but instead, she heads to the train station, where the police are closing in on Young-min. As the police arrest Young-min, Tae-soo submits the keychain as evidence. However, chaos erupts when an officer informs Jung-hwan that Tae-soo is being booked for bribery. They find cash in Tae-soo’s car, leading to his suspension pending investigation. Tae-soo suspects Ha-bin set him up, as she was in his car earlier that day.
Back at the station, Young-min recognizes Tae-soo, shocking everyone, including Eo-jin. The forensic team reveals that DNA from the crime scene matches that on Ha-bin’s keychain, linking both cases and leaving Tae-soo reeling as the episode concludes.
Doubt Episode 4 kicks off with a flashback revealing Min-ah’s involvement in a money exchange for Young-min. She regularly retrieves cash from a hidden mountain stash, until one day, she goes missing with the money. Young-min, suspecting theft, brutally assaults her. Unbeknownst to him, Min-ah did steal the money and hid it in a locker. Meanwhile, Ha-bin has been trailing Min-ah and observing her movements, secretly vowing to kill her.
After the night at the train station, Ha-bin persuades Min-ah and Ji-yeon to flee with her, and they hide in a motel. Ha-bin tries to ingratiate herself with the group, but when Min-ah refuses to share her phone number, Ha-bin becomes enraged, creating a scene. She ends up stealing Min-ah’s phone and secretly installs GPS tracking software. Ha-bin sets a trap by luring Min-ah to the forest to return her phone, choosing the exact location where a villager later discovers the remains of a teen girl. Tae-soo who turned out to be the detective on the case, realizes that Ha-bin might be involved in these eerie events.
The investigation deepens as Tae-soo learns that a former friend of Ha-bin, Lee Su-hyeon, crafted the identical keychains tied to the case. The detectives—Jung-hwan, Eo-jin, and Yong-soo—start connecting the dots between Su-hyeon’s disappearance and Ha-bin’s involvement. Things take a darker turn when Ha-bin, now paranoid, warns Young-min about the police tailing him. Meanwhile, the runaways living with Young-min panic as he grows suspicious of a possible snitch in the group.
At the police station, Eo-jin grows more suspicious of Tae-soo’s connection to Young-min. That night, Tae-soo receives shocking news from a forensic officer: the skeleton found in the forest belongs to Lee Su-hyeon, confirming her tragic fate.
The tension reaches a boiling point when Tae-soo confronts Ha-bin about the keychain linked to Su-hyeon’s DNA. He urges her to turn herself in, but instead, Ha-bin calls the cops on her father, falsely accusing him of domestic violence. As the police take Tae-soo away, Ha-bin coldly tells him to back off.
Meanwhile, Young-min’s grip tightens on the runaways. Tae-soo and Jung-hwan try to corner Young-min in relation to Su-hyeon’s murder, but he denies any wrongdoing. Sung-hee, a neighbor with visible bruises, remains silent about Young-min’s abusive behavior, while Eun-jin, one of the runaways, is locked in the basement, beaten and terrified.
Jung-hwan and the detectives turn to the runaway kids for clues, but they struggle to find solid evidence. Tae-soo tries reaching out to Ha-bin, but she continues to evade him. In a shocking twist, Seok-moon informs Tae-soo that the bribery charges against him have been dropped, clearing his name.
During a tense interrogation, Tae-soo manages to trip up Young-min, getting him to slip up about Su-hyeon’s death. Despite this, the police lack enough evidence to hold him, and he is released. As he leaves, Young-min ominously tells Sung-hee that both Su-hyeon and Min-ah are dead and vows to retrieve his money from Ha-bin.
As the episode progresses, Jung-hwan and Yong-soo interrogate Joon-tae, a key figure in the investigation. Eo-jin and Dae-hong visit Su-hyeon’s house and find a photo linking Su-hyeon to another girl, though her face is destroyed. Tae-soo immediately recognizes the girl as Ha-bin but keeps this information to himself.
Ha-bin contacts Young-min, offering to help him evade the police. Meanwhile, Dae-hong grows increasingly worried for Eun-jin, who is still missing. He visits her, offering protection, but she declines, worn down by empty promises.
Young-min’s attempt to escape police custody leads to a city-wide manhunt. During this chaos, Tae-soo discovers a crucial clue: Ha-bin had only dialed two phone numbers over the past year, both registered under her mother’s name Ji-soo. Upon investigating further, he finds Su-hyeon’s phone hidden in Ha-bin’s study.
In a climactic moment, Young-min confronts Ha-bin, accusing her of killing Min-ah because she extorted money from her late mother, Ji-soo. At the same time, Tae-soo uncovers a video showing Ji-soo burying Su-hyeon’s lifeless body in the forest. The video, combined with Tae-soo’s findings, leaves the episode on a dramatic cliffhanger, with more revelations about Ha-bin’s dark secrets yet to come.
In Doubt Episode 3, the drama intensifies as Detectives Jung-hwan and Yong-soo’s investigation into Min-ah’s murder circles around Ha-bin and her father, Tae-soo. Tension rises when Ha-bin surprises the detectives by opening the door, despite Tae-soo’s efforts to protect her. Ha-bin’s questionable alibi and mysterious connection to several key items, including a suspicious red keychain, continue to deepen the detectives’ suspicions. As clues unfold, Tae-soo’s world unravels with evidence implicating his daughter, suggesting her involvement in a string of sinister events. With each revelation, secrets pile up, ultimately casting Ha-bin and Tae-soo into a web of mistrust, manipulation, and danger. This episode raises the stakes significantly, leaving viewers questioning Ha-bin’s true motives and Tae-soo’s ability to handle the truth.