In the 1950s, shortly after the Korean War, a wandering man named Woo Ryong (Ryu Seung Ryong) and his young son arrive at a remote mountain village on their way to Seoul. To Woo Ryong's surprise, the villagers live in peace and prosperity, especially compared to the rest of the war-torn nation, under the leadership of the strict village chief (Lee Sung Min). There's just one problem: the village is overrun with rats. Woo Ryong negotiates a deal with the village chief to handle the infestation in exchange for money to help pay for medical treatment for his son. However, after Woo Ryong completes the job, the village chief reneges on the agreement and refuses to pay. Deeply upset, Woo Ryong lures the rats back to the village, leading to devastating consequences. This film was inspired by the German folktale "The Pied Piper of Hamelin"

As a child, Park Hoon (Lee Jong Suk) and his surgeon father were spirited away to North Korea to perform a top-secret procedure. However, upon the surgery’s completion, the two were barred from returning home due to political machinations at Myungwoo University Hospital, where Park Hoon’s father worked. Under his father’s guidance, Park Hoon himself becomes a talented surgeon and secretly dreams of fleeing to the South with his lover Song Jae Hee (Jin Se Yeon). Park Hoon and Jae Hee manage to escape, but end up separated – until Park Hoon meets Dr. Han Seung Hee (also played by Jin Se Yeon), who looks just like Jae Hee, at his new workplace, but she denies knowing him. As Park Hoon follows in his father’s footsteps at Myungwoo University Hospital, he must navigate rigid hierarchies, personal mysteries, and a decade-long plan for revenge while also saving patients’ lives.

After overcoming a difficult childhood, Jang Hye Sung (Lee Bo Young) finally succeeds in becoming a public defender. However, she sees her job purely as a way to make money, and tends to push people away with her blunt, jaded personality. Her outlook changes, though, when she unexpectedly runs into high school student Park Soo Ha (Lee Jong Suk) who claims he can help her. Soo Ha developed a strange ability to read people’s minds through eye contact after his father’s murder ten years prior – and teenage Hye Sung, who also witnessed the incident, eventually put the murderer behind bars. Though initially reluctant, Hye Sung allows Soo Ha to stick around, and his ability gives Hye Sung additional assistance in the courtroom. However, when Soo Ha’s father’s murderer is released, Hye Sung and Soo Ha are faced with their most dangerous situation yet.