Barrow, Alaska, a small town on the Arctic circle, is preparing for its annual "30 days of night," a period during the winter when the sun will not be seen. As the town gets ready, The Stranger [Ben Foster], a rather creepy guy, rows ashore from a larger ship, then trudges towards Barrow.
People who don't want to suffer the extended darkness leave for Fairbanks or other parts south. Once he arrives, The Stranger sets about sabotaging the town.
Some time later, the creepy guy steals and destroys all the cell phones, leaving a burnt pile in the outskirts of town.
Barrow's sheriff, Eben Oleson [Josh Hartnett] and his deputy Billy Kitka (Manu Bennett) investigate these crimes. They can make no sense why someone would do this. Eben reasons it couldn't have been a teenager's prank, he believes they would have left a note saying fuck you to the parents or to the world.
Meanwhile, Eben's estranged wife, Fire Inspector Stella [Melissa George], who moved out of town awhile ago, is tending to route duties. Eban is unaware she is in town.
The town prepares for the extended darkness, departing citizens giving farewell hugs to loved ones, the 152 citizens who remain behind.
The Stranger makes his way to the kennel and kills all of the sled dogs.
Eben and Billy return to town to find Beau Brower [Mark Boone Junior], the local snowplow driver who lives alone out on the South Ridge, working on his truck. Eban writes him up a ticket for oil spillage on the town street, as he explains to Billy, a citation once in awhile reminds Beau he is still a part of this town.
Finished with her duties, Stella heads out of town in her truck, but is hit by a tractor in the middle of nowhere, driven by Malekai Hamm (Pua Magasiva). With her truck out of commission, she finally calls Eben to get a ride to the airport. Surprised and disappointed to hear she "sneaked" into town, he sends Billy to give her a ride.
Eben was informed about the canine slaughter and arrives at the kennels. He is greeted by John Riis (Peter Feeney) and his wife, Ally (Min Windle), the couple who manage the kennels. They are enraged someone would commit such a cruel act.
Eben returns to the Sherriff's office, greeted by Eben's teenaged brother Jake [Mark Rendall], and their grandmother, Helen Munson [Elizabeth McRae]. Helen informs Eben of a another vandalism problem at the utilidor.
Stella is too late arriving at the town's airport, she missed the last plane out of town and will have to spend the 30 day period in Barrow.
Eben heads to the utilidor and is greeted by helicopter pilot Wilson Bulosan (Craig Hall) and utilidor operator Carter Davies (Nathaniel Lees). It's implied The Stranger sabotaged Wilson's helicopter, the only chopper in town, by throwing crucial parts into the "muffin monster," the utilidor machine that grinds up metal/junk.
We cut to the Tekcom station, the town's cell tower for telecommunications, manned by Gus Lambert (Grant Tilly). Gus hears noises outside the building and goes to investigate. Shadowy figures surround him, then one attacks and viciously rips out his neck.
At Ikos Diner, the creepy guy gives the waitress, Lucy Ikos (Elizabeth Hawthorne), a hard time because they have no liquor or raw hamburger and makes a scene. By then, Eben steps in and attempts to escort The Stranger out, but he threatens Eben.
Stella has appeared with her gun pointed at the creepy guy's head. He lunges at Stella, but Eben subdues him. Eben handcuffs him and takes him to jail, Stella tags along.
We cut to the pipeline facility where we see Denise (Amber Sainsbury), Gabe (Kelson Henderson), and Aaron (Jared Turner), have finished their shift and are playig around. Suddenly, Gabe is attacked and his bloody body is dumped in front of the other two. Denise runs off and the shadowy figures then surround Aaron.
Back at the Sherrif's office, Eben suspects The Stranger is behind all the vandalism and questions him, but he gives Eben the silent treatment. Eben then disovers pot in a drawer. It's revealed grandma grows it in her greenhouse to help her with her cancer. They then notice they lost internet access and the phones are down.
The creepy guy chimes in, taunting them with "what is coming." At that moment, the power goes down, putting the town in darkness. The sherrif's office is lit again when the back-up generator kicks on. Eben goes to check on Gus at the cell tower. They use walkie-talkies now to communicate.
Eben arrives at the Tekcom station and finds the front door open. He follows a trail of blood that leads to Gus's bloody severed head on a pike.
Eben races back to town, and uses his vehicle's loudspeaker system to warn all citizens to go to their homes.
John and Ally are at home grieving over the loss of their dogs when suddenly a blur of a figure breaks in and drags Ally outside. John tries to rescue her, but Ally is dragged under the building's crawlspace and disappears.
Back at the sherrif's office, The Stranger continues to taunt Stella, Jake, and Helen with, "that's death approaching." The creepy guy manages to trick Jake and now has him in a strangle hold. But Eben shows up and shoots The Stranger, an arm wound. Eben roughs him up and pressures him for answers, but the creepy guy only offers more taunting threats.
Eben and Stella go to investigate the pipeline facility, but they are intercepted by a vampire. Eben shoots at the vampire through the vehicle's roof and they manage to escape.
Eben and Stella head back to town and hear Helen over the radio, screaming. In town, they see a vehicle in flames overturned and hear gun shots. Eben and Stella enter the Sherrif's office and see bloody evidence of an attack, but Jake and Helen are missing. In the jail cell, The Stranger is whining, "they didn't take me," and requests Eben to finish him off. Though tempted, Eben walks away.
The leader of the vampire pack, Marlow (Danny Huston), speaking in an ancient, gutteral language, instructs the other vampires to "not turn" the victims, instead, behead them. He gloats that they should have came to this town ages ago.
Some of the citizens have locked themselves in the diner - Jake, Denise, Lucy, Carter, Wilson, Wilson's senile father Isaac Bulosan (Chic Littlewood), and Doug Hertz (Joel Tobeck). All survivors of the initial attack on the town. They are puzzzled how the creatures keep coming even after shooting them. Jake reveals they killed Helen.
At the home of Adam Colletta (John Wraight) and Jeannie Colletta (Dayna Porter), vampires Marlow and Iris (Megan Franich) capture and kill the couple.
And so begins the second round of slaughter, but on a much bloodier scale. People screaming, vampires shrieking, gun shots, multiple fires - complete mayhem. Unless they are shot in the head, bullets are useless against them, and they feast on numerous citizens of the town.
Eben and Stella reunite with Jake at the diner. They cook up a plan to hide in Charlie Kelso's attic, one of the lucky citizens who left town for the month. Eben asks Carter to lead the group to the attic while he sets out to hunt for supplies to defend themselves, Stella goes along with him.