Heartless City is the tale about the twisted fate of two men and a woman, and pains of love. A newly appointed under-boss of the drug cartel, Shi Hyun is, in fact, an undercover detective who is tasked with conquering the criminal underworld. If he advances just one more step, he can bring in the legendary drug kingpin Chairman Cho and return to being a cop. Yet, the uppermost echelons of the cartel, sense the impending threat and strike back. At the same time, narcotics squad leader Hyung Min loses his girlfriend, Gyung Mi, in an operation meant to bring in Shi Hyun. The desire to take revenge on Shi Hyun consumes him. He sends Soo Min, who was like a sister to Gyung Mi, as an undercover to Jin Sook, who is an associate of Shi Hyun. Undercover as Jin Sook, Soo Min has an intense encounter with Shi Hyun and falls in love with him without realizing who he is. She suffers a torturous dilemma, unable to hold on to him, yet unable to let go of him either. Will Shi Hyun be able to have his revenge in the Heartless City, a world wrecked by the infighting of drug cartels and the competing interests of corrupt prosecutors and cops? Will he be able to protect Soo Min?