Dong Hyeon is a high school student and Pan Soo is a member of a criminal organization. One day, Dong Hyeon falls from the rooftop and falls on top of Pan Soo. Later when the gangster wakes up in the hospital, he finds himself in the body of a teenager.
Jae Ho is the prisoner who makes rules and wields the most power among the inmates. Outside of prison, he was the #2 guy in a criminal gang, but he is ambitious enough to go after the #1 spot upon his release. One day, Jae Ho meets new prisoner Hyun Soo, who doesn't follow the rules of the prison and he doesn't submit to anyone.