Act One

A 17-year-old Mike McDonnell is in his high school gymnasium in a basketball uniform, as the star player of his team ("The Star of Kennedy High"). The pressure is on as Coach Murphy tells him that a scout from Duke is going to be attending the game this evening. As he is playing, his best friend and the team’s water boy, a way less popular Ned arrives as is bullied by the other team members. Shortly after, his girlfriend Scarlet arrives, and Mike sees that there is something off about her. After pressing her, she reveals to him that she’s pregnant. Mike tries to go back to the game but stops short in the middle of the basketball court while the coach, his teammates, and the crowd are cheering him on. Mike drops the ball and leaves the court to go to Scarlet and gives up the game to tell him that they’ll become a family. They walk off the court together, a happy couple.

Seventeen years later, Mike, Scarlet, and their two children Maggie, 17 and Alex, 15 are gathered around the table and lazily sing “Happy Birthday” to Mike. They run off to school as soon as Mike blows out his candles. Mike and Scarlett sit at the table, both lamenting on how their lives have turned out ("Happy Family"). Mike has lost his job and Scarlet tries to encourage him to find a new one to take care of the family. In the middle of their squabble and separate thoughts, Scarlet tells Mike she wants to move ahead with a divorce. This angers Mike who accuses Scarlet of “quitting”. She tells him she is tired of him blaming her for the decisions he made when he was 17 ("Time for Starting Over").

A week later, at Kennedy High School, Alex is getting bullied and getting shoved into a locker by basketball team member Stan Dunbar. Mike arrives at the high school to visit the kids and embarrasses his daughter Maggie. He asks the kids how they’ve been holding up since the divorce announcement and tells them he’s been sleeping at their Uncle Ned’s house. The kids tell him they aren’t surprised at all, and they leave him in the hallway. As Mike starts to leave, he notices the trophy case in the hallway and accidentally bumps into the school’s old janitor.

The Janitor begins to taunt Mike about how his life didn’t turn out how he thought ("Janitor’s Theme") and invites Mike to hold his old basketball trophies. Mike can’t resist and reaches out to touch a trophy, but the moment he does he is unwittingly transformed into his 17-year-old self. He sees Alex and tries to talk to him like father and son, but Alex is frightened of this “new kid” and runs away. Mike looks in the mirror and sees that he is 17 again.

Mike runs off and runs to Ned’s apartment. Mike runs into Ned’s living room and calls out to him, and when enters he sees him and screams. Mike explains what happened at the school with the janitor and Ned is awestruck. Ned tells him that this is a sign for him to follow his true path ("17 Again").

The next day, Mike, now Mark Gold is enrolled as a student at Kennedy High School. The girls known as The Brittany’s begin to flirt with Mark. Ned tells Mark that re-living his senior year in high school maybe isn’t that great of an idea, but Mark insists that he needs to follow the destiny he was meant to have. When Ned asks him what he told Scarlet, “Mark” tells him that Mike went to Peru to find himself. Right as they go to register with fake transcripts and forms Ned made for Mark, Ned runs into Scarlet, and he tells her that he is dropping his “son” off at school. She sees Mark and is shocked that he looks just like Mike at 17. Scarlet laments that Mikes problem was that he never left high school and leaves.

Ned and Mark head into the principal’s office and Principal Masterson arrives. Ned gets an instant crush on her as she reads through the folder with fake information. Principal Masterson accepts Mark into Kennedy High School and Ned tries to ask her out on a date, which she declines ("A Matter of Principle").

The next day, Mark is in gym class with his classmates and tries to introduce himself to Stan, who is a jerk to him. They start to play basketball and Mark is in awe about his abilities to play basketball like a 17-year-old. Stan tried to make him look bad but Mark bests him and makes a winning shot. A now older and almost retired Coach Murphy witnesses this and tells him to come to basketball tryouts and try out for point guard. Mark agrees and revels that his life is going to turn out how it’s supposed to ("Brandnewday").

A little later, Mark calls Ned and tells him that plans are working out and he’s going to try out for the basketball team, meanwhile Ned is determined to win the heart of Principal Masterson. When they hand up, Mark hears someone calling for help in the next stall, and he sees its Alex all taped up. When Mark asks who did this to him, Alex tells him Stan. Mark asks him why he can’t tell his dad and Alex tells him that he wouldn’t understand because he used to be a jock. When Mark tells him that things will get better and he must find his niche, Alex tells him to forget it ("Losers Never Win").

Later, Mark and Alex go to the cafeteria to eat lunch together and while they’re talking about Chelsea, a girl Alex likes, Stan starts in on Alex, bullying him in front of Mark and the cafeteria. Mark has enough of Stan's torment and stands up to him, embarrassing him in front of the other students. The other students laugh and cheer ("The New Guy at Kennedy High").

Later at the O’Donnell house, Scarlet’s best friend Naomi comes to take her out. As Scarlet leaves, she knocks on Maggie’s bedroom door and tells Maggie to look after the house and Alex. As soon as she leaves, Stan comes out from under her bed and tries to seduce her while they’re supposed to be studying ("Gonna Show It to You"). Meanwhile downstairs, Mark and Alex are playing basketball and Alex is surprisingly great at it. When Mark asks where Maggie is, Alex tells them studying with Stan, but they’re really hooking up. When Mark hears this, he sounds off the house alarm and stops them. Maggie comes downstairs and Mark lectures her about dating a loser like Stan and letting her college dream of Georgetown go to stay with him. She rebuffs his command to dump him and storms away. When Mark asks Alex where their mom is, he tells them out with their Aunt Naomi at a place called Caliente.

Mark goes to Caliente to find Scarlet and Naomi there ("Make the Most of Tonight").

Mark confronts Scarlet about the kids and Scarlet says that Mike is to blame. Naomi and Scarlet have Mark kicked out of the bar, and Mark begins to lament about his choices with a vision of Older Mike by his side. He laments that he took his family for granted and he should have been fighting for them ("The Greatest Prize").

Act 2

Basketball tryouts are beginning and Mark invites Alex to try out with him ("Take a Shot"). At the O’Donnell home – Scarlet tells Maggie that she can’t just throw her life away for Stan. Maggie tells her that just because she made a mistake marrying Mike, doesn’t mean that she will and runs off. Alex and Mark come into the house and Alex tells Scarlet that he made the team. When Scarlet tells him to call his dad, he tells him he won’t pick up. Meanwhile, Mark apologizes to Scarlet about the night at the bar and she forgives him and tells him that she’s glad he’s looking out for her children, and that their dad isn’t around. Alex comes back and tells Scarlet that Mike didn’t pick up, but Mark tells him that his dad would be proud of him anyway. Scarlet is disappointed that Mike didn’t pick up and talks to Mark about the divorce ("Happy Family Reprise").

The next day, Ned comes to Principal Masterson’s office again to try to win her over, but she rebuffs his advances again. He begs her and makes a deal that if they go on one date, he won’t bother her again and she agrees.

Later at the O’Donnell house, Scarlet and Naomi are getting Scarlet ready for a date. They start to finish up when Mark takes Scarlet aside and shows her the backyard where he has built a hammock that Mike never finished. It is surrounded by trees with twinkly white lights. Scarlet says she has to go and finish getting ready for her date, and that he’s taking her dancing. Mark tells her to practice with him, and he picks the song that she and Mike danced to at their wedding. They dance together and she imagines Mike at the age they are now and gets carried away with the music ("Love You Till Forever"). Mark almost goes in for a kiss, when Alex shows up with Scarlet’s date, Dean. As they are about to leave Mark tells Scarlet that she can’t go out with him because of Alex, and how he would be confused seeing her run around with so many men. She is rightfully offended and walks off with Dean. Mark asks Alex is he’s okay with this and he says yes because he wants to see his mother happy, and it’s not like his dad cares or is fighting for her. Mark tells him that his dad wishes he could be here.

The next day, Chelsea talks to Alex but he is completely awkward with her. Mark tells him that he’s going to give him a second chance with her. He tells him to meet him at his place, and then tells the Brittany’s he’s throwing a party. He then runs into Maggie who tells him that Stan dumped her and reveals that she only went out with him to freak out her parents. Mark tries to comfort her and tells her that she deserves better ("You Deserve the Best").

That night, Ned and Principal Masterson go out to a fancy restaurant. Ned tries to woo her with expensive things, and she shuts him down, saying that when he was a loser, he was probably a nicer guy. He asks for a second chance, and they find how that they have some “nerdy” things in common ("Tra La La"). They agree to go home together after a romantic evening.

That same night at Ned’s house, there is a party happening and the teenagers are destroying everything in sight ("Nothin’ Like a Party Part 1").

Meanwhile, Mark finally sets Chelsea and Alex up. Mark looks for Maggie and he sees Stan trying to get back together with her, she says no, and Mark comes in to tell him to leave. He taunts Maggie and Mark throws a punch at Stan who hits him. He falls back into Maggie’s arms, and Maggie tries to kiss him ("Nothin’ Like a Party Part 2"). He backs away and tells her that he likes a different girl, the same girl since he was 17.

Scarlet comes to the party to look for Alex, and Mark tells him he’s fine and he might be leaving the party with his first girlfriend. Scarlet thanks him for looking after Maggie and Alex and just as Ned and Principal Masterson walk in, Mark kisses Scarlet. Scarlet slaps him, runs away, and the party ends. Maggie and Alex are disgusted, and believe Mark was only nice to them to get to Scarlet.

The next day, Ned goes to the O’Donnell house to try to convince Scarlet not to go through with the divorce. Scarlet begins to leave with Naomi to get to the courthouse, but Mark stops them and reads Scarlet a letter from Mike ("Something So Perfect"). He leaves and when Scarlet looks at the letter, it's revealed to be a math test and that it was truly Mike all along. She runs into the house and tells Naomi to postpone the court date. Mark gives up and goes to the high school basketball game and tells Ned that he’s going to live the life he thought he was supposed to have.

At the basketball game, everyone is ready to play and cheer, and Scarlet and Maggie sit at the game. Scarlet tells Maggie the last time she was here, Mike proposed to her ("The Star of Kennedy High Reprise Part 1"). Ned sees Principal Masterson and they make amends and sit at the game together ("Tra La La Reprise"). The game begins and Coach Murphy motivates the team ("The Star of Kennedy High Reprise Part 2"). Scarlet can’t watch “Mark” play and runs out of the gym, and Mark follows her, passing the ball to Alex who scores the winning shot. Everyone cheers and Mark runs through the halls, to see the Janitor again. Mark looks through the trophy case and he is himself again. He finds Scarlet and they reconcile ("Something So Perfect Reprise"). Maggie and Alex come out to find their parents in love again and they all share a happy moment ("Brandnewday Reprise").