As a young child, Nora Tidemann (Ine Marie Wilmann) is captivated by stories told by her father, Tobias (Gard B. Eidsvold), who introduces her to the fascinating mythology of trolls. One story leaves a lasting impression as he recounts a particular troll wedding where 13 drunken trolls lost track of time and turned to stone, becoming the formidable mountains that now loom over Dovre. Years pass, and a tragic incident occurs when a drilling operation for a railway project leads to an explosion, resulting in the deaths of numerous workers and protestors.
In a bid to uncover the truth, the Norwegian government, led by Minister of Defense Frederick Markussen (Fridtjov Såheim) and Chief of Defense General Sverre Lunde (Dennis Storhøi), enlists a team of scientists, including the now-grown Nora, who has become a paleontologist eager to make her mark. As the team investigates the eruption, they initially blame it on a methane pocket, but only Nora and the Prime Minister's advisor, Andreas Isaksen (Kim Falck), observe the large footprints surrounding the site. This prompts Prime Minister Berit Moberg (Anneke von der Lippe) to authorize further exploration with the aid of military soldier Captain Kris Holm (Mads Sjøgård Pettersen).
Nora, driven by a deep intuition that something truly mythical might be awakening, seeks the expertise of her father, Tobias, who has retreated into seclusion after suffering the consequences of his beliefs regarding the existence of trolls. Despite his past struggles, he examines the findings and footage from the eruption site and proposes a radical theory—that trolls once roamed the earth before their extinction due to the spread of Christianity in Norway. Tobias shows evidence that suggests the emergence of a troll, and the four of them inadvertently rouse the sleeping giant, capturing irrefutable video proof of its existence.
As the governmental attempts to subdue the creature fry into chaos, conventional weapons prove ineffective, and tragically, Tobias meets his end while trying to empathize with the troll. During this turmoil, Nora recalls tales of trolls repelled by church bells and recommends a sonic attack; however, this only angers the troll further, wreaking havoc across the countryside. With the media broadcasting the unfolding crisis, the Prime Minister reluctantly decides to evacuate Oslo to prevent greater calamity.
Nora discovers plans for a nuclear strike against the creature, leading her and Andreas to attempt to halt the operation based on revelations from Tobias' research. They learn from Chief of Court Rikard Sinding (Bjarne Hjelde) that the history of trolls has been suppressed and that the Royal Palace sits atop the ruins of the Troll King’s palace where his family met their demise. Realizing the creature's intentions align with returning to its true home in Oslo, she develops a plan to utilize the sun's destructive rays against it—a vulnerability confirmed from their research.
As emotions run high and the stakes grow, Nora and Kris work together to create a trap using UV light from tanning beds while Andreas coordinates with Sigrid (Karoline Viktoria Sletteng Garvang) to delay the nuclear strike. The duo lures the troll with a skull into their trap, but at the crucial moment, Nora hesitates, seeking to preserve the troll's life. Nevertheless, the rising sun signals an inevitable fate for the massive creature. With the devastation left in the wake of its passing, a sense of wonder fills the air—what else may be lurking within the mountains of Norway?
As silence blankets Oslo, a rumble echoes from the depths of the Dovre Mountains, leaving the audience to ponder if trolls might still be hidden away, waiting for the right moment to emerge once more.
