Park Yeong-han, a detective with a reputation for apprehending small-time offenders in the province, joins 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 recruits the fiery Sangsun, the mighty Gyeonghwan, and the elite Hojeong to Unit 1.

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.