In 1989, 17-year-old Mike O'Donnell learns from his girlfriend Scarlet Porter that she is pregnant during the start of his high school championship basketball game. Moments after the game begins, he leaves the game and goes after Scarlet, abandoning his hopes of playing college and professional basketball.
In 2009, Mike, now a 37-year-old, finds his life stalled. Scarlet has separated from him due to his regrets about abandoning college, forcing him to move in with his geeky and wealthy best friend since high school, Ned Gold. At his job, we see another reason for his frustration: due to his lack of higher education and since he is significantly older than most of his co-workers and he is passed over for a promotion he deserves in favor of a much younger female worker. He gets fired from his job (after smashing his boss's bluetooth earpiece against the wall) and his high school-age children, Maggie and Alex want nothing to do with him. Later, while visiting his high school to reminisce, an encounter with a mysterious janitor transforms Mike into his 17-year-old self.