Popular high school senior Mike O'Donnell (Zac Efron) seemingly has it all. He is a star athlete headed straight for a college scholarship when he decides to give it up to settle down with his high school girlfriend Scarlet is pregnant.
Twenty years later, an adult Mike (played by Matthew Perry) finds his life is not exactly what he expected. He is separated from his wife, Scarlett (Leslie Mann) and living with his wealthy software genius nerd and best friend Ned Freedman (Thomas Lennon), his career at a pharmaceutical company is at a stand still, and his relationships with his teenage children are nonexistent. After getting passed up for yet another promotion at work, he returns to his high school to reminisce over his basketball awards and the life he could have had. While he is reliving his glory days, he is approached by a janitor and shares with him how things were so much better when he was 17.
As Mike is driving home from the high school, he sees the mysterious janitor standing on the ledge preparing to jump into the Los Angeles River. Mike rushes out of his car to rescue him, but when he gets there, the janitor has vanished. What Mike doesn't realize is that he is about to fall into the river and turn into his 17 year old self.
Young Mike (Zac Efron) returns to Ned's house, where he has the difficult task of convincing Ned that he is in fact Mike. At a loss of what to do, Ned pretends to be Mike's father and they register Mike back in high school to finish the life he never had the chance to live.
High school presents a lot of new challenges for Mike, such as dressing cool, keeping up with the latest gadgets and making new friends. But nothing compares to being in high school with his own children. He discovers that his daughter, Maggie (Michelle Trachtenberg), is not nearly as innocent as he thought she was and his son, Alex (Sterling Knight), is the brunt of the star athlete's jokes.
But Mike's most difficult realization is that he hasn't been a very good father or husband. Mike befriends Alex and tries to instill him with enough confidence to join the basketball team. He gets close to Maggie's obnoxious boyfriend and does everything in his power to break them up. Most importantly, he visits an unsuspecting Scarlet and rediscovers all the things that initially made him fall in love with her. You don't know what you have until you lose it.
Through his experiences, Mike realizes that he had chosen the perfect life he just never appreciated it. Now, he must figure out a way to transform back into his older self and win back his wife and kids. *Info from comingsoon.net*
In 1989, Michael O'Donnell was the star of the high-school basketball team, with a college scout in the bleachers ready to watch his championship game and a scholarship guaranteed for him if he played well. Just as the game is about to start, he sees his girlfriend Scarlett by the bleachers. He blows her a kiss, then goes to her when she looks very troubled. She tries to pretend everything is fine, but finally she tells him she's pregnant. The game starts, but he can't think of anything but Scarlett, and when he sees her leaving, he tosses the ball away and walks away from the game and the scholarship to marry her.
Twenty years later, Mike's life is a mess. Scarlett has separated from him, forcing him to move in with his high-school best friend Ned Gold, now a geeky millionaire software developer, and his kids Maggie and Alex are distant and want nothing to do with him. At his job, his boss passes him up for a promotion in favor of a woman the boss likes who's far less competent, and Mike explodes at the boss and is fired. He stops by his old high school on the way home, sees his 1989 team photo in the showcase, and reminisces about the life he threw away. Then he encounters a mysterious janitor who asks him if he really wishes he was a teenager back in high school again, and he does. On the way home, he sees the "janitor" apparently ready to jump from a bridge and he tries to stop him, but the janitor suddenly disappears and Mike falls in the river himself, where he's magically transformed back to age17.
After he convinces Ned who he really is, Mike decides he's been given the chance to live his life over again "but to do it right" -- to win the basketball scholarship and go to college. With Ned posing as his father, he re-enrolls in high school under the name "Mark Gold," living with Ned in his mansion full of high-tech toys. But as he starts to fit in to school life, he realizes his daughter is dating the sadistic basketball captain Stan, who only wants sex from her, and that Stan is also bullying and tormenting his son. Gradually, "Mark" realizes that the real reason he's been given another chance in life is to help his children and try to win back Scarlett's love. He befriends Alex and discovers that his son has real talent in basketball and can hit 3-point shots effortlessly. He works with Alex to sharpen the rest of his game so he can win a place on the team and the girl of his dreams. As Alex and Mark practice shooting baskets together every day at Alex's house, Scarlett is amazed how much her son's new friend looks like her ex-husband looked in 1989.
Mark starts helping Scarlett landscape her back yard, because she hopes to start a landscaping business. He gains a new appreciation for her talents, but he frequently comes close to her or touches her in ways she considers inappropriate between an adult woman and a teenaged boy. He also comforts Maggie when Stan dumps her for refusing to "put out." He tells her that someday she'll find a guy who treasures her the way she deserves, but he's horrified when he realizes Maggie is starting to think that guy is HIM. He tells her he can't get involved with her because he's already in love with someone else, someone secret.
The basketball team wins a come-from-behind game, with Mark doing a lot, but Alex makes the winning 3-point shot. Meanwhile, Ned has been smitten with Jane, the high school principal, since the first day he went to her office to enroll his "son," but his geeky attempts to impress her have done nothing but disgust her. Finally, in return for buying laptops for all the students in the school, she agrees to go to dinner with him on the same night that Mark has announced a party at his house to celebrate winning the game. Mark tells only certain people about the party, but kids text it everywhere and the whole school shows up.
Ned's romantic dinner with Jane is going nowhere until he finally admits that he's always been a loser with women. He's really just a geek, obsessed with The Lord of the Rings. She slowly smiles, and starts talking to him in Elvish -- one of the languages in The Lord of the Rings -- and he realizes that she's also a Lord of the Rings fanatic. After a seductive conversation in Elvish, Ned and Jane go back to his house for romance, but they find Mark's party completely out of control with hundreds of kids everywhere. Scarlett is also there, looking for Alex, and Mark's feelings for her are so strong that he can't control himself and he tries to kiss her in front of all the kids. Scarlett is appalled and slaps him, then runs away with Mark following her, shouting that he's her husband and the father of her children. Maggie and her friends all see this and are disgusted, especially Maggie, because Mark had told her he was in love with someone secret, and now she sees him trying to kiss her own mother.
The next morning, cleaning up the chaos after the party, Ned reminds Mark that the hearing for Mike O'Donnell's final divorce decree with Scarlett is in 20 minutes, and they rush to the courtroom. Ned pretends to be Mike's lawyer, and they're being thrown out when Mark says he's there to read a letter that Mike has written to his wife. Scarlett agrees to hear the letter, and Mark reads it with emotional power in his voice that astonishes her, plus details about their courtship that only her husband could have known. Mark finishes by saying that, since he sees that she doesn't want him in her life anymore, he's content to let her go because he loves her so much. After Mark finishes and is forced to leave the courtroom, Scarlett picks up the "letter" and discovers it's just a piece of paper with directions to the courthouse on it. Mark wasn't reading a letter at all but somehow knew all the things he had told her. She asks for the divorce decree to be postponed.
Mark tries to forget about Scarlett and concentrates on basketball, because winning the scholarship and going to college seem to be the only thing he has left for him. On the day of the championship game, where Mark and Alex are playing and Maggie is cheerleading, Scarlett is looking at her high-school yearbook and realizes that Mark doesn't just look similar to her husband at 17, he looks EXACTLY the same. Then Maggie reminds Scarlett she's supposed to drive her to the game, and Scarlett stays to watch.
As the game is about to start, Mark sees Scarlett in the bleachers. He blows her a kiss, using a gesture identical to the one Mike had used in 1989, when he was playing in the same championship game and saw her standing by the bleachers. Scarlett finally realizes that Mark really IS her husband, somehow turned 17 again. She realizes all the reasons she loved him then and still loves him, but she knows she can't possibly make her life together with a 17 year-old boy. Also, she realizes that knowing she's there in the bleachers watching him could put him in the same situation as before, and she can't risk making him lose his college scholarship again. She leaves, going down the same corridor she used when she left the game in 1989.
Mark sees Scarlett leaving, forgets about the game and walks away, just as he did in 1989. He hands the ball to Alex, saying this time it's his turn, and runs down the corridor after Scarlett. We see the mysterious janitor smiling in the stands, and by the time Mark catches up to Scarlett, he's the adult Mike O'Donnell again. Mike tells Scarlett he's made a mess of his marriage because he spent the last 20 years resentful at her for losing him his chance to go to college, but now he realizes his family is the only thing that matters to him, and he asks for another chance.
A few days later, Mike goes to Ned's house to get his stuff and return his key. He finds Ned in bed with Jane, both of them wearing Elf ears. Mike thanks Ned for all he's done, and Ned gives Mike a parting gift, a whistle for his new job, because Jane has made Mike the new coach of the high school basketball team.