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Police transport officer, Kim Yeong-goon, comes across a suspicious man whilst on traffic control. His suspicions lead to a chase and an internal investigation to an even more suspicious network.

Chi-kwang and Yeong-goon find out the suspicious man has kidnapped Chairman Kim's daughter. The two must locate her before too late with the help of the man.

The child is located, and possibilities of corrupt police open up an investigation. The teams first assigned task is organ trade.

Prosecutor Lee arrests all those involved beating the internal corruption investigation team to it. Police and prosecution agree to stop the investigation but internal corruption investigations team continue their work.

Kim Jae-myeong requests his son Yeong-goon for a visit for the first time in 15 years and gives him a tip to help him with a promotion. He hands him a ledger relevant to Oh Sang-gon, but angers Yeong-goon.

Sang-do suffers a critical wound and is taken to hospital. Tae-joo notices a thumb with a scar like hers in front of Oh Sang-do's hospital room and goes to verify it. Meanwhile, Yeong-goon searches for Sang-do's missing wife.

6 dead bodies are found in a park. Chi-kwang is successful in identifying one of the bodies and the investigation kicks off. All bodies except one are missing thumbs.

Yeong-goon questions his memories of the night of his mother's murder. He becomes unsure if it was his father.

Yeong-goon's father passes away and a funeral is held. Yeong-goon suspects his father's killer to be Chi-kwang but hopes he is wrong. Meanwhile, Tae-joo notices Jae-myeong's body without a thumb and Yeong-goon receives a call from Baek Song-yi.

Yeong-goon assists Chi-kwang to investigate Goryeo Cleaning Company for its suspicious meddling in a case. However, Yeong-goon finds it difficult to trust Chi-kwang. Meanwhile, Tae-joo uses the ledger to threaten the district attorney.

Jae-myeong hid the ledger and Yeong-goon finds it inside his shoe. Yeong-goon opens the ledger waiting for Chi-kwang and Tae-joo.

Ambitions are revealed and the Commissioner is aided by Tae-joo during investigation, escaping narrowly. Meanwhile, Yeong-goon finds new evidence.

Tae-joo catches the turtle with her hands and leaves the internal corruption investigation team. Yeong-goon re-opens a 15-year-old murder case.

Chi-kwang tortures Jin-woo to reveal the culprit that killed Yeong-goon's mother 15 years ago. Chi-kwang is successful in interrogation and locates where Yeong-goon and Tae-joo are held.

Yeong-goon remembers everything of the night his mother died. He visits the perpetrator's house to arrest him but instead persuades him to turn himself in.

Yeong-goon is shocked at findings that indicate his father created the extraordinary network. He is left with a choice to decide the directions of the remaining investigation.