The show opens in Treegap, New Hampshire, where the various characters name what they want most in the world: Winnie Foster, to go to the fair; Mae Tuck, to see her sons again; Jesse Tuck, to take in the familiar sights of Treegap; Miles Tuck, to be unstuck in time; and the Man in the Yellow Suit, to "learn the secret" of Treegap Wood and become immortal ("Live Like This"). Winnie goes into her house, where she spends most of her time with Mother and her grandmother now that her father has died. She wishes for a life bigger than their living room and wants to explore Treegap Wood ("Good Girl, Winnie Foster"). After running outside once again, Winnie encounters a parade led by the Man in the Yellow Suit that leads to the fair ("Join the Parade"). Desperate to see the fair, Winnie Foster opens the gate and runs into the Wood after the faint sound of a music box ("Good Girl, Winnie Foster (Reprise)").
There she meets Jesse Tuck, who drinks from the spring. To keep her from doing the same, Jesse offers to show her what he calls the top of the world, as seen from the trees ("Top of the World"). After, he and Miles kidnap Winnie and bring her back to the Tucks' house to keep her from revealing their secret. Back at the Foster home, Mother has called on Constable Joe and his son Hugo to search for Winnie ("Hugo's First Case, Parts 1 and 2"). The Tucks, across the wood from the Fosters, tell Winnie the history of the Tuck family, and how they have become immortal by drinking the water in Treegap Wood ("The Story of the Tucks").
Winnie stays the night with the Tucks and, while finding clothes for Winnie to wear, Mae tells her the story of the day when her husband, Angus proposed to her ("The Most Beautiful Day"). Winnie decides that staying in the Tuck family's attic is its own kind of adventure ("The Attic"). Still, she eventually decides to sneak out with Jesse to go to the fair ("Join the Parade (Reprise)").
At the fair, Winnie and Jesse play games and decide to become friends that travel the world together ("Partner in Crime"). They leave the fair and sit on top of the magical tree, where Jesse convinces Winnie to drink the water when she turns seventeen so they can be married ("Seventeen"). The Man in the Yellow Suit overhears Jesse's speech and decides to follow the Tucks to get to the enchanted water.
The Man in the Yellow Suit celebrates his victory with those from the traveling fair ("Everything's Golden"). Back at the Tucks' house, Winnie contemplates Jesse's proposal ("Seventeen (Reprise)"). The Tucks discover that Jesse has asked Winnie to drink the water and become angry with him. Winnie talks to Miles about his son Thomas, whom Mae mentioned earlier, and Miles shares how he has not seen Thomas in eighty years ("Time"). The Tucks then lament what it means to be stuck in time forever, and aim to live more fully in the coming years ("Time (Reprise)").
The Man in the Yellow Suit visits the Fosters and convinces Mother to give Treegap Wood to him if he can safely bring Winnie home ("Everything's Golden (Reprise)"). Constable Joe and Hugo see the Man leaving the Foster home, and remark that you can't trust a man dressed in yellow ("You Can't Trust a Man").
Angus takes Winnie fishing and attempts to convince her to live a mortal life instead of drinking the water with Jesse ("The Wheel"). Miles approaches and tells them that Jesse has gone without saying goodbye, and Winnie says they can find him at the spring in Treegap Wood. There, Jesse encounters the Man in the Yellow Suit who tells him of his long journey to find the spring and forces Jesse to take him there ("The Story of the Man in the Yellow Suit"). The Tucks and Winnie find Jesse, and the Man in the Yellow Suit offers to make them partners in his water-selling business. After the Man takes Winnie as a hostage, Jesse offers him a vial of water in exchange for her; before he can drink it, however, Mae hits him on the head with a rifle and kills him instantly. When Constable Joe and Hugo arrive, Winnie tells them that she killed the Man in the Yellow Suit when he tried to pull a knife on her and Jesse.
Close to being exposed, the Tucks leave town on the advice of Constable Joe. They say goodbye to Winnie and offer her their music box, thanking her for reminding them that there is "still something to live for." Jesse says he will leave instructions on how to find him and leaves her with a vial of water from the spring. Winnie contemplates drinking the water and what it means to live forever ("Everlasting"). She ultimately decides to live out her mortal life and pours the water on a toad instead.
Through a ballet sequence, the ensemble shows the remainder of Winnie's life: she marries Hugo and has a son, while her grandmother, Constable Joe, and Mother pass away one by one. Before she dies, Winnie opens the Tucks' music box and dances one last time at the gate of the Foster home as she did when she was young.
The Tucks return to Treegap after Winnie has died to discover her grave, which is dedicated to a "cherished wife, devoted mother, and dearest grandmother." They celebrate the fact that she lived a full life and encounter the toad Winnie made immortal with the water from the spring ("The Wheel (Reprise)").
