The Townspeople of Arendelle and the royal family — Queen Iduna, King Agnarr, Young Elsa, and Young Anna — celebrate summer ("Let the Sun Shine On"). As the princesses play, Young Anna goads Young Elsa into using her magical powers to create ice and snow, but Queen Iduna reminds them that magic must stay secret.

Later that evening, the sisters create a magical toy snowman named Olaf ("A Little Bit of You"). As their games grow more adventurous, the Snow Chrous joins in and Young Elsa accidentally strikes Young Anna with her powers. The King and Queen rush to help, and Queen Iduna calls on the Hidden Folk to revive Young Anna ("First Joik"). Pabbie and Bulda, the mystical leaders of the Hidden Folk, remove the ice from Young Anna's head as well as all memories of Young Elsa's magic.

Young Elsa grows fearful of her powers and isolates herself from her sister until she can learn to control them; the gates to the castle are closed. With no memory of the magic strike, Young Anna wonders why her sister will no longer play with her ("Do You Want to Build a Snowman?").

Years later, Middle Elsa still struggles to control her powers as her fear grows, while Middle Anna still yearns for her sister's affection. The King and Queen leave the kingdom to search for answers but are lost at sea.

On the day of Elsa's coronation as queen, the Castle Staff reopen the gates. Anna daydreams about how exciting it will be to have life back in the castle, while Elsa practices controlling her powers for the coronation ("For the First Time in Forever"). As guests arrive, Anna bumps into the charming Prince Hans, and both of them slam into Kristoff, a local ice harvester, and his reindeer, Sven, knocking Kristoff's bag of ice to the ground.

The Bishop crowns Elsa as she contemplates the relationship she wishes she could have with Anna ("Dangerous to Dream"). At the coronation ball, the two sisters finally talk and laugh together, particularly at the expense of the arrogant Duke of Weselton. Later, Anna finds Hans, and the two immediately fall in love ("Love Is an Open Door") and decide to marry. The elated couple asks Elsa for her blessing of their marriage, but she refuses. As tensions rise, Elsa accidentally shoots ice into the ballroom. Elsa flees, and Anna runs out to find her.

On the snowy mountainside, Kristoff sings a song to Sven ("Reindeer(s) Are Better Than People") when a freezing Anna comes upon them. They agree to help her find Elsa, and are startled when Olaf, a magical snowman, appears. Olaf vows to help them bring back summer, and along with the Summer Chorus, fantasizes about what it will be like ("In Summer"). The group also comes across Oaken and Oaken's Family, who teach them about hygge and provide them with winter gear ("Hygge").

Isolated in an ice palace of her own making, Elsa lets go of her fear and embraces her powers ("Let It Go"). Meanwhile, Hans and Weselton send out a search party to find Anna and capture Elsa.

Anna, Kristoff, Sven, and Olaf finally find Elsa. Elsa's newfound liberation doesn't last long, however, once Anna reveals that her powers have set off an eternal winter everywhere. In her panic, Elsa accidentally strikes Anna again ("For the First Time in Forever – Reprise"). When Elsa blasts the group down the mountain ("Mountain Fall"), they seek a cure for Anna from the Hidden Folk ("Kristoff's Joik"), who think she and Kristoff are a couple ("Fixer Upper"). When Anna faints, however, Pabbie and Bulda inform them that only an act of true love can thaw her frozen heart, so they return to Arendelle to find Hans.

Meanwhile, Elsa is captured and brought back to the castle. When Anna arrives, Hans reveals that he never loved her and was just using her to become King of Arendelle. He leaves Anna to freeze to death, but Olaf helps her escape to find Kristoff.

Hans tells the kingdom that Anna has died and sentences Elsa to death, who, in her fear, creates a massive blizzard ("Colder by the Minute"). As Anna is about to reunite with Kristoff, she sees that Hans has drawn his sword over Elsa. Anna sacrifices herself, stopping Kristoff's sword as she turns to ice.

This act of true love between sisters thaws Anna, and Elsa realizes that love can thaw the effects of her powers ("Finale – Part 1"). Anna sends Hans away, and the kingdom celebrates while all vow to fill the world with light and love ("Finale – Part 2").