Plot

Deep in the Dovre mountain, something gigantic wakes up after a thousand years in captivity. The creature destroys everything in its path and quickly approaches Oslo.

Deep inside the mountain of Dovre, Norway, something gigantic awakens after being trapped for a thousand years. Destroying everything in its path, the creature is fast approaching the capital of Norway, with city-dweller struggling to stop something they thought existed only in Norwegian folklore.

As a young girl, Nora Tidemann's (Ine Marie Wilmann) father, Tobias (Gard B. Eidsvold), teaches her the mythology of Trolls (at a troll wedding, 13 drunk trolls lost track of time and got exposed to sunlight and turned to stone. Those stones became the troll mountains) and the origin of their local mountains. During one story, Nora almost "sees" the faces of trolls turned to stone in the rock face.

Years later, a drilling operation tunneling through the mountains of Dovre (to build a railway line through the mountains) results in an eruption and the deaths of several workers and protesters. Desperate for answers, the Norwegian government (led by Minister of Defense Frederick Markussen (Fridtjov Saheim) & Chief of Defense General Sverre Lunde (Dennis Storhoi)) recruits a diverse array of scientists, including Nora, who is now a Paleontologist on her first major find. While the collected scientists initially believe that the eruption was caused by the miners hitting a pocket of Methane, only Nora and the prime minister's advisor, Andreas Isaksan, (Kim Falck) point out that the region is surrounded by large impressions that appear to be footprints. The Prime Minister Berit Moberg (Anneke Von Der Lippe) permits them to investigate the possibility further with Norwegian military soldier, Captain Kris Holm (Mads Sjogard Pettersen), when a second incident miles away tears apart the home of an elderly couple.

Nora begins to believe that a Troll may be responsible and the three seek assistance from Tobias (who lives a secluded life in the middle of nowhere), who has since lost his professorship for his belief in the existence of a real basis for mythical creatures and was in a mental institution for a while. Tobias looks at the evidence and the video footage of the railway tunnel site, which indicates a hominid blasting its way out of the mountain. He theorizes that trolls freely roamed the Earth more than a 1000 yrs ago. They went extinct with the Christianization of Norway. He was close to revealing it all, when he was put away in a mental asylum.

After a quick search of the mountains, Tobias identifies a topographical anomaly and the four accidentally awaken the slumbering Troll, having camouflaged itself on the mountainside. They escape, capturing the first tangible video proof of Nora's theory. The prime minister arranges a military operation led by Kris; however, conventional weapons like tanks, grenades and guns only annoy the troll. Tobias tries communicating with the troll but is killed when the creature is startled by more gunfire. The troll continues to move towards Oslo. Researching the mythology, Nora recommends a sonic attack using church bells (she infers from mythology that the Church deployed its bells as a weapon against the trolls), but it enrages instead of incapacitates the creature, causing immense collateral damage. Following the rampage, international news outlets have picked up the story and broadcast it globally.

As the troll heads to Norway's capital Oslo, the prime minister orders a complete evacuation of the city. After learning of the government's plan to destroy the troll with a nuclear bomb on Oslo, Nora and Andreas object, but are dismissed from the task force. Nora makes a last attempt to find out the truth about the creature. Tobias' notes lead them to the Royal Palace, where they meet Chief of Court Rikard Sinding (Bjarne Hjelde), who reveals the truth about trolls in Norway. Tobias had been right all along; Trolls had been living in Norway until they were wiped out by Christian settlers and the truth buried in folklore. When Nora's father got too close to the truth, Sinding had him discredited and committed to a mental health hospital. The Royal palace was built on top of the Troll King's palace after the Christians massacred his family and left him for dead inside a cavern in the Dovre mountains. Nora concludes that the creature is heading for Oslo in an attempt to return home. Nora discovers that the bones of the trolls incinerate under UV light. She and Andreas theorize that the troll can be stopped by exposing it to direct sunlight.

Discovering that trolls are vulnerable to direct sunlight, Nora and Kris plan to expose the troll to UV light from a number of tanning beds. While Kris calls on fellow soldiers to make the troll trap, Andreas asks his friend Sigrid (Karoline Viktoria Sletteng Garvang) at the secret government facility to delay the bombing of Oslo. Sigrid hacks into the military's system to halt the nuclear strike. Nora and Andreas place the skull of one of the troll's babies in the back of the Queen's truck and lure him to the UV light trap. Nora has a last-minute change of heart, turns off the lights, and tries to save the creature's life. However, the sun then rises into a clear sky and kills the troll. While everyone else rejoices, Andreas and Nora wonder if more trolls are still alive deep inside Norway's mountains.

In the aftermath, something seems to emerge with a roar from the rubble inside the Dovre Mountain cave.