17岁的迈克(扎克·埃夫隆 Zac Efron 饰)是校园风云人物,在一次关键性的篮球冠军赛上,他决定放弃前途,向怀有身孕的女友斯佳丽求婚。20年后,人到中年的迈克(马修·佩里Matthew Perry 饰)生活事业两失意,妻子斯佳丽(莱斯利·曼恩 Leslie Mann 饰)决定与迈克分居,一双儿女也对他形同路人,迈克只好搬入科技新贵的朋友奈德(托马斯·列侬 Thomas Lennon 饰)家暂住。迈克追忆自己本来可有的锦绣前程,却在重返高中校园过程中遇到一位神秘的清洁工,让他突然重返17岁。迈克决定与奈德假扮父子,重入高中,相信这是上天给他第二次机会让他做出正确决定,却发现自己的女儿玛吉(米歇尔·崔切伯格Michelle Trachtenberg 饰)与儿子亚历克斯(斯特林·克耐特Sterling Knight 饰)在学校问题重重……At 17 Mike O'Donnell is on top of the world: he's the star of his high school basketball team, is a shoo-in for a college scholarship, and is dating his soul-mate, Scarlet. But at what's supposed to be his big game where a college scout is checking him out, Scarlet reveals that she's pregnant. Mike decides to leave the game and asks Scarlet to marry him, which she does. During their marriage, Mike can only whine about the life he lost because he married her, so she throws him out. When he also loses his job, he returns to the only place he's happy at, his old high school. While looking at his high school photo, a janitor asks him if he wishes he could be 17 again and he says yes. One night while driving he sees the janitor on a bridge ready to jump, and goes after him. When he returns to his friend Ned's house, where he has been staying, he sees that he is 17 again. He decides to take this opportunity to get the life he lost.