Profiler Park Hae-young caught the fragmented call through the static of a discarded two-way radio – his own name, distorted and faint. Then, a voice began to speak, detailing a case long closed, a puzzle with no solution.

With the suspect in custody, the statute of limitations is suspended. Hae-young joins Soo-hyun’s team, formed to tackle the burgeoning backlog of unsolved cases.

The course of events shifted irrevocably after Hae-young shared information with Jae-han. Driven by a newfound understanding, Hae-young resolved to collaborate with him in 1989, determined to avert the impending tragedy.

Won-kyung, the woman Jae-han loves, is the ninth victim. A driver has surrendered to the authorities, but Soo-hyun and Jae-han are convinced that the true killer is his son.

Hae-young begins to investigate Jae-han’s vanishing. His former colleagues grow wary at the sight of her delving into his history.

Haunted by the circumstances of his daughter's death, Kyung-tae emerges from prison after serving time for burglary, consumed by a desire for retribution. He then orchestrates a kidnapping, driven by a vengeful purpose.

Jae-han apprehended Se-kyu in connection with the string of burglaries, yet the accused was released after a brief incarceration. Meanwhile, Kyung-tae continued his pattern of violence, perpetrating further murders.

A subtle link began to form in Soo-hyun and Hae-young’s minds, a thread connecting the current burglary to the tragedy of Da-hye, the woman who had taken her own life two decades prior.

Hae-young discovered that Chi-soo and Jae-han first encountered each other in 1999, while working a case in Inju. Following their imprisonment for the crime, Hae-young’s brother took his own life.

The bodies found in the mountains seem to be further victims of the serial killer who terrorized the region in 1997. Jae-han discovers that Soo-hyun has been promoted to team leader.

Convinced of Jin-woo's guilt, Hae-young and Soo-hyun apprehend him. Afterward, Hae-young turns to Jae-han, seeking information regarding the rape committed in Inju.

With increasing scrutiny, Hae-young finds herself implicated in the death of Chi-soo. Meanwhile, Jae-han arrives at a clear understanding of the true instigator behind the assault on Hye-seung.

A wave of grief washed over Soo-hyun and the others as they confirmed the remains were indeed those of Jae-han. Hae-young, meanwhile, discovered a poignant detail: Jae-han had once been a guardian to Soo-hyun.

The revelation from Hye-seung – that Sun-woo was innocent – sparked a chilling possibility in Hae-young's mind: that his brother had been murdered.

The arrest of Hae-young for Chi-soo’s murder sent a chilling ripple through the city. Meanwhile, Soo-hyun listened to Jae-han’s voice on the radio, a somber apology for his inability to avert Sun-woo’s fate.

Hae-young’s condition is critical following a shooting that occurred during a meeting with Sung-bum. In 2000, Jae-han was captured by Bum-joo.