The town of Barrow in Alaska, is isolated in eighty miles of roadless wilderness. Once a year, they spend thirty days of winter in complete darkness known as "the polar night". Near this town, the Stranger arrives on a boat, and after staring at a creepy ship in the distance, he makes his way to Barrow. Outside Barrow, sheriffs Eben and Billy find a pile of burnt phones buried in the snow, which doesn't look like a prank. They also take the chance to look at the last sunset they'll have for a month. In town, people are getting ready to either hibernate or leave on the next plane. Since everyone is so busy, they don't notice a mysterious figure sneaking into the local kennel and killing all the snow dogs in it. Back to the sheriffs, they stop to check on Beau, whose bulldozer is leaking gas all over the snow. Eben is in the middle of fining him when they get a radio message reporting the death of the dogs. Meanwhile, Eben's ex-wife Stella finishes her job and takes her car to the airport.
In the middle of the road she's suddenly hit by a bulldozer, destroying her car. Stella can't wait to be towed and calls Eben for help, but Eben uses the excuse of having to work to avoid her and sends Billy to pick her up instead. Billy drives Stella to the airport as fast as possible but they still don't make it in time, so now Stella will have to stay a month in Barrow. Back to Eben, he looks at the dogs and finds a complete massacre, but the owners Ally and John can't think of anyone that could hate them this much. Afterward, Eben returns to the police station, where his grandmother Helen and his brother Jake work with him. They receive a message from the utilidor reporting some vandalism, so Even goes to check it out. Carter and Wilson explain someone destroyed their helicopter, which is usually kept under lock and key. Meanwhile in the cell tower, Gus hears some strange noises outside and goes to check them out, only to notice the lights going out.
A group of mysterious figures suddenly surround him but before Gus can react, these people jump on him and kill him in order to feed - it turns out they're vampires. In the town's diner, the Stranger tries to order a raw burger and something to drink, but the waitress explains they have a law that doesn't allow them to sell alcohol during the dark month. The stranger starts making a scene but fortunately Eben and Stella arrive at the same time to stop him from getting violent and take him to the station's cell. In the meantime, a group of pipeline workers is finishing for the day when suddenly, one of them gets dragged into the darkness. A few seconds pass before the worker's body falls on the snow, causing his friend to run away in panic. The third worker's frozen in fear, and the vampires take the chance to surround him. Back at the station, Eben tries to find out how the Stranger sneaked into their town, but the man refuses to answer.
Suddenly the internet goes out, and when Eben tries to call Gus, he discovers the phone lines are out too. At that moment the entire town also loses power and the Stranger announces "they" are coming. Eben goes to the cell tower to find out what's going on and finds a trail of blood that he follows until he discovers Gus' head. Horrified, Eben rushes back to town and drives around to tell every citizen to stay inside. If they don't have a generator, then they should hide in the diner. In John's house, Ally is preparing dinner when suddenly a vampire breaks through the window and drags her out. John hears her screaming and goes to save her with his rifle, but when he gets close enough, the vampire scratches to keep him away. Unwilling to give up, John tries again and even manages to grab Ally's hand, but the vampire's stronger and takes her away. At the station, the Stranger keeps talking about the end coming for everyone. Jake gets annoyed and throws a piece of his game at him, but this only makes the Stranger happy because he can use it to pick the lock. Immediately Jake goes to retrieve the piece and the Stranger uses the chance to attack him, but at that moment Eben arrives and shoots the Stranger in the arm. Then he handcuffs the man to the cell door to interrogate him, but the Stranger's only answer's that they'll all die. Eben asks Helen and Jake to say inside while he and Stella look for the criminal. After a few minutes of driving, Eben stops the car because he saw something, but when Stella checks with her binoculars, she gets scared and urges Eben to get back in the car. The pair tries to escape, but a vampire suddenly jumps on top of the car, and Eben shooting at it does absolutely nothing. Stella stops the car, and this does make the vampire fall, allowing them to return to town. When they get back, they see fires everywhere and hear gunshots. Helen contacts them through the radio to ask for help so they hurry back to the station, but it's too late. Helen and Jake are gone, only having left a trail of blood behind.
The Stranger is still in the cell complaining because "they" didn't take him and asks Eben to help him end things. Eben truly considers killing him, but Stella stops him. Meanwhile the vampires gather in town to hear from their leader Marlow. He reminds them it's important to remove their victims' heads to prevent them from turning into vampires too. He also wishes they had come to this town sooner because the constant darkness is perfect for them. Then the vampires go on a killing rampage around town, feeding on anyone they can put their hands on without mercy. A horrified group of survivors gathers in the diner and all share the same experience: their bullets did nothing. Eben and Stella arrive and are relieved to see Jake is ok, but unfortunately Helen didn't make it.
The group discusses their options and Carter suggests hiding in the utilidor, but that's too risky because it's too far. A woman points out that her neighbor has an attic with a hidden pull-down ladder and the house was boarded up before the owner left. Eben asks Carter to guide the group to that house while he and Stella distract the vampires. The two of them drive around town to act as bait and the plan works, soon a bunch of vampires grab their car and try to attack them through the windows. Eben manages to kill one of them by aiming at the head, but Marlow takes his gun and the car gets flipped over. The vampires immediately reach for Stella and Eben again, but at that moment, Beau shows up in his bulldozer and runs over the enemy. Eben and Stella rush to join him in the vehicle and they drive away rather fast until they make it to the house with the attic, which is incredibly well hidden as promised. Eben tells the group they'll sleep in shifts and ration their food, they have good chances of surviving because they're used to the polar night unlike their enemy.
Meanwhile Marlow and Iris visit the Stranger at the station. They commend the man for doing his job perfectly and promise to turn him, but when Marlow hugs the Stranger, he kills him instead. Six days pass with the survivors managing to stay alive and well in the attic, although sometimes they have to deal with Wilson's father Isaac having dreams about his wife, who died years ago. One evening, they hear noises outside, and Stella looks out through a hole to discover the vampires are ransacking the neighboring houses. Some of the survivors want to leave before they're caught, and when Stella and Eben point out it's too risky, an argument ensues. Eben calms everyone down and reminds them they're team before coming to terms with the fact the vampires are too close.
They need to escape to gather supplies from the store and hide in the utilidor, but they'll need some cover, thus they agree to try when the next blizzard comes. On day seven, the group hears Kristen walk down the streets asking for help. Eben notices the vampires follow her by jumping on the roofs, meaning they're using her as bait. The survivors insist on helping her, so Eben comes out and discovers John is around too, hiding underneath a house. Kristen is his priority and Eben asks John to wait, but unfortunately this distraction means Eben doesn't make it in time and the vampires begin slashing at Kristen before jumping to feed. With the vampires distracted, Eben goes to save John, but as soon as he pulls him out he notices John is becoming a vampire too. Eben tries to talk to him but John goes rabid and attacks, pushing Eben against a swing set that catches him with its chains. Fortunately there's an ax nearby that Eben uses to defend himself, allowing him to kill John with a few precise strikes. Then Eben runs back into the house, where he collapses from an asthma attack. Outside, Marlow finds John's body and takes it as a clue of someone being around.
Moments later, it's Stella's turn to be on guard, and Isaac takes advantage of her falling asleep to leave the basement. Stella and Wilson hear the door and immediately go after him, convincing him trying to walk to the city is a terrible idea. Isaac cries as he thinks his wife won't survive and goes to the bathroom. However seconds later they hear a noise and discover the door's locked. Wilson picks the lock and they discover Isaac has escaped through the window, so Wilson goes after him and pushes Stella away when she tries to stop him. Eben hears the commotion and comes down to check on Stella, but at that moment, a vampire enters the house and they hide in the bathroom. The vampire looks around the house and approaches the bathroom door, but when he's about to open it, he hears Wilson calling for his father outside and decides to go after him instead.
While Wilson gets killed, Eben and Stella run back to the attic, feeling guilty for abandoning their friend. Suddenly thumping noises can be heard from the roof, Eben looks through the window and confirms not only that the vampires are gone, but that it's also snowing heavily. Using the wind and snow as cover, the survivors go to the local store to gather as many supplies as they can carry. Suddenly they hear a noise and to their horror, they find a vampire girl feeding on a body. The survivors run to find Eben, but when he comes closer with his ax, the girl's gone. Eben keeps looking around, and the girl comes out of the shadows to attack him, making him drop the ax. The rest of the group quickly comes to help him, grabbing the girl together and pinning her against the wall in order for Jake to kill her with the ax, a task that leaves him deeply traumatized. The survivors get ready to leave, but they discover it's stopped snowing, so they'll have to wait inside the store for another blizzard. On day eighteen, Eben points out they need to leave because the vampires will soon reach this area.
The utilidor's still too far to reach without cover, thus they agree to go to the police station, but they need a distraction. They realize the vampires sent the Stranger to cut communications off early on because they couldn't come out during the day, and Eben remembers Helen had UV lights for his plants in her house, so he'll fight the vampires with those while the others run away. Eben runs out of the building making noise on purpose to get the vampires' attention, however one of the creatures goes after the fleeing group and jumps on one of the survivors. The group has no choice but to leave him behind as they escape, safely making it to the station. The vampires surround Helen's house and Marlow allows Iris to go first, but as soon as she steps inside, Eben receives her with the glowing UV light. Iris falls on the snow as half her body burns and the vampires go to shut down the generator to turn off the lights. Eben runs through the back door while he keeps his group updated through the walkie-talkies, so Beau tells him to run to Rogers Avenue. Marlow sees Iris suffering and gets her permission to feed on her so she can die in peace. The other vampires follow Eben only to suddenly be run over by Beau driving a ditch driller. He shoots all the ones that try to jump on the vehicle, but soon there are too many of them and Beau decides to crash the driller into a building. Then he leaves the vehicle with a box of explosives in hand, and since his rifle is jammed, he lights a flare and drops it in the box. Eben watches the explosion that takes down a bunch of vampires before running away in grief, however Beau is still alive. When he comes out of the building, Marlow calls him pathetic and kills him with his foot. Eben joins the others at the station, but their reunion is cut short when Carter reveals he was bitten by the girl in the store when they held her down. Carter lost his family in a car crash and has wanted to end things for a while but he never dared, now he finally has a reason to ask for assistance.
Eben hates to do this but knows it's for the sake of their own safety, so he takes Carter into another room to kill him while everyone hears. On day twenty-seven, they notice a light coming from a neighboring house. Eben and Stella go to check and are shocked to find Billy next to the bodies of his family after he killed them to save them from the vampires. He wanted to end things for himself too but the gun jammed. Eben scolds Billy for not having even tried to save his family before the three of them return to the station, only to find it empty. Since it's started to snow again, the trio assumes the others went to the utilidor and begin heading there. When they hear some noises, they hide under a house and see Gail coming down the street. Stella rushes to grab her and bring her under the house right before a vampire appears, so Eben decides to distract him to give the others a chance to escape.
However instead of going with the girls, Billy runs in another direction in fear, getting another vampire's attention. Eben manages to run safely to the utilidor and reunites with the others, but he worries when he notices Stella and Gail haven't arrived yet. Meanwhile Marlow gathers the vampires and reminds them humans shouldn't know they're real, meaning it's very important to find every single survivor and kill them all. Back at the utilidor, Billy arrives without knowing a vampire's following him. The beast bites Billy and the group quickly comes to help him when they hear the screams. This vampire's stronger and manages to overpower Eben, almost throwing him into the metal grinder. Billy jumps on the creature and pushes it into the grinder first, effectively killing him but also losing his arms in the process. To make matters worse, Billy is starting to turn, so Eben has no choice but to kill him too. On day thirty, the survivors begin to celebrate that the sun will come out soon. Eben finally manages to contact Stella through the walkie-talkie, and she explains she and Gail are hiding under a car nearby.
Eben checks through the window and sees they're surrounded by vampires, so he asks Stella to wait under the car until morning and they can see the sunrise together. However the vampires are tired of waiting and used the oil that Beau's bulldozer leaked all over town to start a fire. If Stella and Gail stay under the car, they'll burn, but if they come out, they'll be killed. A desperate Eben realizes a human can't win this fight, so he uses a syringe to take some blood from Billy and injects it into his own body. As Eben begins to turn, the others wonder if they should kill him, but a crying Jake protects his brother. Eben says goodbye to Jake with a hug, then goes outside to challenge Marlow to a one-on-one fight. Marlow accepts and begins beating Eben up easily, but this distraction gives Stella and Gail the chance to escape. Eben's body continues to change while he's being pulverized, and when Marlow's about to deliver the final blow, Eben's eyes turn black. He uses his new full vampire strength to hit Marlow's head so hard that he instantly kills him. Having lost their leader, the other vampires run away, but Eben doesn't go after them because it's almost dawn. Stella realizes the sunlight will affect Eben too, so she takes him to the top of the hill. The couple shares one final kiss as the sun comes up and turns Eben into ashes in Stella's arms.