Park Yeong-han, a detective with a reputation for apprehending small-time offenders in the province, comes to Seoul's Jongnam Police Station in 1958. He goes straight after the Dongdaemun gang, a bunch of political goons who attack a market vendor.
Yeonghan and Sangsun attempt to apprehend smugglers but get hindered by corrupt Jongnam officers. Yeonghan plans to take them all down, but it puts him in danger from the Dongdaemun gang, making him seek refuge in a bookstore.
Unit 1 is tasked with clearing beggars off the streets, but Yeonghan sees an opportunity to gain allies; Unit 1 employs beggars to discover the thieves' plan to target a prominent bank when a bank robbery occurs in the provinces.
Unit 1 takes on a case of a missing baby and find ten infant bodies during the investigation. Yeonghan connects with the case and uncovers unsettling truths about the Angel House orphanage, confirming suspicions about the director's murky history.
Yeonghan secures evidence to arrest Viper with the help of a store owner's daughter. However, he is released shortly afterward owing to false testimony and lack of proof.
A newcomer steps into the fold; Senior Superintendent Choi hopes promotion at the Public Security Department; former military police officer Baek Doseok becomes the next Senior Superintendent of Jongnam Police Station.
As Yeonghan probes deeper into a suicide he witnessed on 1962, doubts emerge; despite Doseok's interference, Yeonghan persists with his team's investigation, uncovering a crucial witness and hidden truths beyond the apparent suicide.
In a desolate alley late at night, three drunk pedestrians become victims of consecutive attacks, leaving one unconscious from severe assault. Unit One takes on the case while also responding to a murder report.
When Yeonghan receives a report of a missing female factory worker, he suspects the wealthy factory owner and apprehends him, but Doseok releases the suspect without further interrogation; a woman's body is found at the foot of a cliff.
