Pan-soo is a career criminal and a savvy entrepreneur who is the son-in-law of a mob boss. After a freak accident, Pan-soo wakes up to find out that his body had been swapped with that of a 17-year-old boy, Dong-hyeon. Trapped inside a teenage body, Pan-soo realizes that Dong-hyeon had been bullied in school, and that he had gotten into the accident while trying to protect a girl. While trying to fix some of Dong-hyeon's problems, he discovers that he now has the chance to fix his own past mistakes.