Dae Ho can purposefully control his dream environment while lucid dreaming.
His child gets kidnapped, and in order to unpack the facts he’s buried in his memory, he has to get the help of someone who can send him back into his dreams while half-awake. They race against the clock while poking around in his dreams for clues about the crime, which he collects in bits and pieces.
Jung Se Ro is a hardworking young man who works multiple part-time jobs while studying for the foreign civil service exam. His father is a petty criminal and a con man, and their family lives a transient life because of his deals, currently staying in Thailand.
Despite wanting an honest life for himself, Se Ro's dreams are shattered on the night of a glamorous jewel exhibition opening in Bangkok. His father dies in an incident involving stolen diamonds, and because Se Ro was at the scene when another man was shot, he is accused and arrested for murder. After spending five years in a Thai prison, upon his release he takes up a new identity and becomes a con man just like his father. He joins a ring of jewel smugglers led by Park Kang Jae, with whom he shares a brotherly bond. Kang Jae was raised like a son by Se Ro's father, who taught him all the tricks of the trade. But Kang Jae has harbored a lifelong jealousy towards the real son, which is stoked further when the woman he loves, smuggling accomplice Seo Jae In also falls for Se Ro.
Then Se Ro meets Han Young Won, the cold-hearted heiress to a jewelry brand. She was madly in love with her fiancé Gong Woo Jin, and had closed herself off after his death. But Se Ro draws her out into the world, while Young-won gives him a reason to live when he had all but given up. They fall in love, not knowing that the man Se Ro was accused of killing had been Young Won's fiance. His love for her becomes his punishment, but also his salvation.
In the spring of 1978, Hyun Soo transfers to Jungmoon High School in Gangnam where his mother thinks the land price will skyrocket due to the development of the area. Yet, Jungmoon High School is notorious for its severe corporal punishment by teachers and power struggles between school gangs. On the first day, he gets spanked with an aluminum baseball bat for violating the school's dress code. Then, one day, he plays basketball with his classmates and brings his team a victory, which allows him to become chummy with Woo Sik, a kingpin of the school. Before long, they find out that they both are huge fans of Bruce Lee and become best friends.
After school, on the bus, Hyun Soo and Woo Sik see a girl who resembles Olivia Hussey, the most popular foreign actress in Korea at that time. Her name is Eun Ju, a senior at a nearby girls high school. Both fall in love with her at first sight. Hyun Soo is gentle and kind, while Woo Sik is tough and charismatic. Knowing Woo Sik is so different from her, she can't help but becomes attracted to him.
Hyun Soo endures the pain of his secret love for Eun Ju. However, Eun Ju and Woo Sik begin to bicker over petty things. While she's in pain over Woo Sik cheating on her, Hyun Soo sees a chance to win her heart. In the meantime, Woo Sik and Jong Hoon, a student patrol captain, get into a fight. In the duel, Jong Hoon cheats and beats up Woo Sik, who leaves school in the aftermath of his defeat. With Woo Sik gone, Jong Hoon abuses his power as student patrol captain and bullies whoever gets in his way. Hyun Soo falls into an Inferior Class, and Jong Hoon keeps bullying him. The corporal punishment and favoritism by the teachers gradually become worse. To make matter worse, Eun Ju chooses Woo Sik over him. Driven to the wall, Hyun Soo explodes. With nunchakus tucked in the back of his pants, he goes up to the roof after Jong Hoon.