Doubt

Tae-soo, a legendary criminal profiler, goes home while working on a case to celebrate his daughter's birthday. However, he is called to a police substation to pick up his daughter who got herself in trouble. Later, Tae-soo realizes that Ha-bin could be involved in a murder case and starts doubting her.

To avoid repeating the nightmare of the past, Tae-soo wants to trust his daughter. However, every piece of evidence he comes across reveals traces of Ha-bin. What could Ha-bin be trying to keep secret? Meanwhile, during his investigation, Dae-hong discovers that Tae-soo is involved in this case.

Jung-hwan and Yong-soo visit Ha-bin at her place to interrogate her and see Tae-soo there. Tae-soo goes around trying to check Ha-bin's alibi on the 11th. He finds dashcam footage of Ha-bin that goes against her alibi. Ha-bin suggests to Tae-soo that they move, but Tae-soo insists on staying until he catches the real culprit. Meanwhile, cops find a stash of cash in Tae-soo's car and accuse him of accepting bribes.

A chilling discovery unfolds as a seemingly innocent keyring from Ha-bin reveals the possibility of a serial murder case. Tae-soo grows increasingly anxious, sensing that Young-min and Ha-bin are hiding something crucial. Just as the tension rises, the police arrive at Tae-soo's home once again, intensifying the fear of what secrets might be uncovered.

Tae-soo gets a call from his wife, who died one year ago. As Tae-soo learns about Ji-soo's shocking secret, Joon-tae becomes increasingly apprehensive as the investigation progresses. Meanwhile, Ha-bin, who believes her mother is a murderer, begins to dig deeper into her mother's past as an unidentified man follows her from behind.

A man who claims to be Song Min-a's dad appears before Ha-bin and demands to know about her relationship with Choi Young-min. Ha-bin learns from him that Tae-soo helped Young-min escape from the police. The police raid Young-min's place and take all the kids for questioning. Ha-bin finds where Young-min is and hears who killed Lee Soo-hyun and why.

At the scene of Choi Young-min's murder, a woman's necklace is found. Knowing it belonged to his wife, Tae-soo worries it might put Ha-bin at the scene. Later, Tae-soo visits Park Joon-tae after learning that Joon-tae personally knew Choi Min-ah, and the man claiming to be Min-ah's father shows up at Sung-hee's place to question her about the day Min-ah died. Meanwhile, the police station realizes there is a connection with Ha-nin.

Park Joon-tae testifies that he was the only one at the scene when he murdered Choi Young-min. Tae-soo brings Sung-hee to the interrogation room and pushes Park Joon-tae, and he confesses that he killed Song Min-ah to protect Sung-hee. Meanwhile, the police find out whom the necklace found at Choi Young-min's crime scene belonged to.

The violent crimes team identifies Ha-bin as the prime suspect in Choi Young-min's murder. As Captian Oh and the chief order him to step away from the investigation, Tae-soo finds himself in a position without any possible way to make things work. He tries to stop Ha-bin's investigation but soon encounters the shocking truth through Ha-bin's confiscated items.

Tae-soo and Ha-bin find out what really happened to Ji-soo. Tae-soo wants to find the CCTV footage that could be crucial in catching the real culprit, but Ha-bin is against it. Ha-bin thinks it's only right to take revenge on the real culprit for her late mom, but Tae-soo doesn't agree with her.