17-year-old Mike (Zac Efron) is a schoolboy who proposes to his pregnant girlfriend Scarlett at a crucial basketball championship game. 20 years later, Mike (Matthew Perry) is frustrated with his career and life. His wife Scarlett (Leslie Mann) decides to separate from him. His children are also strangers to him. Mike has to move in with his friend Ned (Thomas Lennon), a tech upstart. Mike recalls the bright future he could have, but he encounters a mysterious cleaner in the process of returning to high school, which makes him suddenly return to the age of 17. Mike decides to pretend to be a father and son with Ned and re-enter high school, believing that God has given him a second chance to make the right decision, but finds that his daughter Maggie (Michelle Trachtenberg) and son Alex (Sterling Knight) are having problems at school...