The plot of "17 Again" follows Mike O'Donnell as he reverts to the age of 17 following a freak accident. Mike re-enters high school, intent on not making the same mistakes he made in his youth.
Mike O'Donnell, played by Matthew Perry, is a 37-year-old man with two children. He is separated from his wife, Scarlet, played by Leslie Mann, and is forced to live with his best friend, Ned, played by Thomas Lennon. When Mike goes to his old high school to reflect on the past, a mysterious janitor transforms him back into his 17-year-old self, played by Zac Efron.
Mike returns to high school and is instantly popular. He also uses his popularity to help his children: Maggie, played by Michelle Trachtenberg, and Alex, played by Sterling Knight. Conflict arises when Mike reveals to Scarlet that he has become 17 again, which causes an even greater rift in their relationship. The film ends with Mike convincing Scarlet of his identity by using a mysterious note, which contains information only Mike could know. Scarlet reunites with Mike at the high school, at which point Mike returns to being his 37-year-old self. Mike is then hired as the high school's new basketball coach.