[5][6] Set in the 1990s, The Worst of Evil follows undercover police investigators who infiltrate a massive criminal organization responsible for the illegal drug trade between Korea, China and Japan.

Park Jun-mo is a senior patrol police officer in the countryside who is constantly belittled by the in-laws for having a lower rank and career prestige than his wife, Yoo Eui-jeong, an elite member of the Security Division of the Seoul Metropolitan police.

Sick of being emasculated by his job, he accepts a deal as an undercover cop in the Gangnam organization so he can get a promotion that matches his wife's prestige.

In response, Jang slams a bucket of water in Gi-cheul's face, rebuffing the suggestion as he does not want to endanger his business by getting involved in narcotics.

After the attack, Gi-cheul meets with Song Dong-hyuk, the mob's 'big boss', to gain his blessing to take over the Gangnam territory and promises him 50 million won in profit every month if he allows the trading of narcotics.