The film begins with young Anna (Hadley Gannaway) and Elsa (Mattea Conforti) joyfully playing in an enchanted forest created by Elsa’s magical snow creations. Their father, King Agnarr (Alfred Molina), and mother, Queen Iduna (Evan Rachel Wood), enter, with Agnarr recounting a tale from his youth about a real enchanted forest he once visited with his father, King Runeard (Jeremy Sisto), and other Arendellian soldiers. In this forest, they encountered the four elemental spirits: Earth, Fire, Water, and Air. However, the joyful tale turns sour as Agnarr remembers the conflict with the Northuldra tribe that led to his father’s death and his own brush with danger, only saved by a mysterious being. As he finishes his story, Queen Iduna sings a gentle lullaby to the girls, titled "All Is Found."
Fast forward to the present day, where Elsa (Idina Menzel) is drawn to a melodic voice only she can hear. Meanwhile, Anna (Kristen Bell) joins Olaf (Josh Gad) outside as he rambles about the changes in their world, but Anna reassures him that changes are fine as long as she has her loved ones around her, boldly stating, "Some Things Never Change." Kristoff (Jonathan Groff) confides in his reindeer, Sven, about his plans to propose to Anna.
Their cozy night takes a turn when Elsa hears the mysterious voice again, causing her distress and prompting her to leave the room. When Kristoff attempts to find the perfect moment to pop the question, Anna's worry about her sister takes precedence. After reassuring Elsa, they both retire for the night. However, the voice persistently calls to Elsa, compelling her to explore its source, questioning its origin and the deeper secrets lying within her powers, which she learns with the song "Into The Unknown."
Arendelle soon descends into chaos, experiencing significant weather disturbances – fierce winds, empty fountains, and extinguished lanterns. In a show of leadership, Elsa guides the citizens to safety. The group seeks guidance from Grand Pabbie (Ciarán Hinds) and the trolls, who inform Elsa and Anna that the spirits of the Enchanted Forest are angered and demand reparation for past grievances. Determined, Elsa resolves to confront these issues alone, but Anna, along with Kristoff, Olaf, and Sven, insists on accompanying her.
After traveling far from Arendelle, they reach the mystical Enchanted Forest, shrouded in a thick mist that traps them inside. The group gets separated amid the confusion, leading Olaf to express his bewilderment through the song "When I Am Older." The Air Spirit creates a tornado that separates them further, yet Elsa attempts to quell its rage using her ice powers. In the chaos, she glimpses flashes of memories, including one of young Agnarr, which culminates in a calm interaction with the spirit, which Olaf affectionately names “Gale.”
As they navigate the forest, they encounter a Northuldra tribe led by Yelena (Martha Plimpton) and Arendellian soldiers headed by Lt. Destin Mattias (Sterling K. Brown). Olaf amusingly recounts their previous adventures, while they soon face an attack from the Fire Spirit. With her ice abilities, Elsa overcomes the flames, only to discover the spirit is actually a small, adorable salamander named Bruni. After the group hears the mysterious call once again, it becomes clear that their mother, Iduna, had a Northuldra ancestry, creating a bond that softens tensions between the Arendellians and the Northuldra.
As the journey unfolds, Kristoff meets Ryder (Jason Ritter), a Northuldra who shares his appreciation for reindeer care, while Elsa strikes up a friendship with Ryder's sister, Honeymaren (Rachel Matthews). Honeymaren enlightens Elsa that there exists a fifth spirit connecting the elemental powers. Meanwhile, Kristoff struggles to find the right moment to ask Anna for her hand in marriage, while he is together with Ryder, who tries to help him devise a grand romantic proposal.
Eventually, the group discovers the wreckage of Agnarr and Iduna's ship. From their water-powered memories, Elsa learns her parents died trying to understand her magical abilities, and finds evidence that they were headed to the mythical river of Ahtohallan. Determined to uncover the truth, Elsa insists on going alone to Ahtohallan, pushing Anna and Olaf away in an ice boat, which leads to conflict and frustration as they feel abandoned.
As Elsa makes her way across the waters, she faces challenges posed by the Water Spirit, known as a Nokk. Upon taming it, she follows the voice, leading her to her family’s past through her memories, where Iduna’s voice calls out. She learns of Runeard's treachery against the Northuldra and his murderous actions against their leader. When Elsa ventures too deep into Ahtohallan, she turns to ice, but not before imparting her revelations to Anna. As Olaf fades away, he reiterates their bond, highlighting their love before his departure. Struck with grief but fueled by resolve, Anna vows to act to save both Elsa and Arendelle.
Anna realizes that destroying the dam is crucial, even if it risks flooding Arendelle. Rallying the Earth Giants, she convinces Mattias to aid her mission. With a collaborative effort, they break the dam, unleashing a wave towards Arendelle. Restored by Anna's actions, Elsa rides the Nokk back, freezing the waters to save the kingdom and lifting the mist around the forest. The soldiers and the Northuldra are freed, allowing for a united front.
In a heartfelt reunion, Elsa and Anna embrace, brimming with love and relief. Kristoff finally manages to propose to Anna in a sweet moment, which she warmly accepts. The now unified Northuldra and Arendellians express their gratitude towards the sisters, celebrating the newfound friendships.
Returning to Arendelle, Anna takes her place as queen, while Elsa chooses to remain in the forest where her powers are cherished. The sisters commit to maintaining their bond across the distances, with Elsa often visiting the enchanted Ahtohallan, riding on the Nokk.
