In the near future, planet Earth is suffering an extinction level event, 300,000 survivors are selected to board a spaceship called The Ark which will take them to a new colony called New Earth in another solar system several light years away. Noah (Cody Kearsley) stows away on the Ark impersonating a junior janitor while his pregnant girlfriend Hayley (Kassandra Clementi) is put into stasis as a passenger.A grizzled older mechanic named Clay (Bruce Willis) attempts to mentor Noah. Blue (Johnny Messner) and Shady (Johann Urb), two experienced mechanics, are infected by a parasitic force. Meanwhile, Noah spies on Clay and suspects the older mechanic is constructing a bomb. Clay shows Noah that he is brewing moonshine and not building a bomb.That evening, the workers have an impromptu party where they tell each other about the loved ones they left behind. Noah tells everyone how he will be reassigned to be a butcher when they reach New Earth. Ortega (Angie Pack) leaves the party to hook up with Blue and finds him welding alone. Blue turns on Ortega, killing her.Later, Clay discovers that Noah's girlfriend is Admiral Adams' (Thomas Jane) daughter. Security officer Stanley (Timothy V. Murphy) discovers Shady's decomposed body and identifies Blue as the killer. Clay finds Ortega's body while the search for Blue continues. Stanley gathers a security detail and they find Blue attempting to break into the admiral's quarters. Clay tries to reason with Blue while Stanley demands his surrender. Things take a turn when Blue leaps and kills one of the security team by biting through the officer's throat. Stanley and Teek (Callan Mulvey) are forced to shoot Blue dead. Chambers (Rachel Nichols) performs an autopsy on Blue's body to find out why he killed Ortega and Shady. Teek meanwhile searches the video feed and sees a recording of Shady's death and Blue's initial infection. Chambers reports that Blue is completely hollowed out and there is a parasite loose on the ship.Chambers discovers that Noah is not a member of the crew but a stowaway and Stanley arrests him, believing Noah to be involved in the strange goings-on. Clay defends Noah successfully and he is released. While the survivors discuss next steps, the three dead crewmen reanimate and attack, killing Stanley. Chambers manages to injure the remaining infected in order for Teek, Clay, and Noah to escape. The newly infected Stanley starts to release the infected and unlocks the remaining crew's quarters who are quickly taken over and infected.Clay guides the survivors to the arsenal. Chambers is unable to pinpoint a weakness in the infected so Clay suggests using a flame thrower. The flame thrower sets off the fire suppression unit which ruins visibility. Lincoln (Corey Large) reunites with the group just as Teek is suddenly grabbed by the infected and pulled into the mist. Clay runs off to rescue Teek. As Teek and Clay return, Lincoln suggests using the escape pods while Teek proposes the security bay.Lincoln manages to launch an escape pod. But as it leaves the ship, he is shown not to be alone and is killed off-screen. The remaining survivors get to the security bay but Stanley nabs Clay as they try and lock themselves in. Noah shoots Stanley before he can infect Clay and they barricade the door.With 84 days until the Ark reaches New Earth the survivors try to concoct a plan to fend off the infected and save the rest of the passengers. Clay guides Noah through the air ducts to the Admiral who they hope will be able to rescue them. Teek then confesses that he was the one who unleashed the infection. Noah reaches the Admiral and Teek confesses to Clay and Chambers that he is responsible for everything that has transpired and is in reality a misanthropic hard-line revolutionary who is against the re-population of New Earth.The Admiral awakens his security team and proposes to use stronger weapons against the infected. As the infected break into the security room Clay and Chambers fight them off while Teek is attacked and killed. The Admiral's security team are eventually overwhelmed and Blue chases Noah. As they fight, Noah splashes Blue with cleaning fluid and Blue collapses screaming. As Noah attempts to tell everyone of his finding, the Admiral sacrifices himself by setting off a grenade, seemingly blowing the infected apart. But just as Chambers and Clay think it's over they notice the remaining body parts starting to reconnect.The infected form a stronger mutant being and the other infected enter the reactor core. Noah explains the effect the cleaning fluid has and the group head to Clay's moonshine stash to construct better weapons. Just as they are planning their attack, the time to arrival starts to decrease as the infected manipulate the reactor. Clay attacks some infected with his newly constructed weapon. The infected start to infect the passengers. Clay sends Noah to rescue Hayley while he holds off the infected. Clay rescues Hayley and they make their way towards an escape pod just as the mutant infected being attacks. Chambers is killed in the monster's first attack as Clay attempts to hold it off but he too is overwhelmed and seemingly killed.Noah and Hayley make for the remaining escape pod, but Noah has to separate from Hayley to start the launch sequence. He confronts the monster and manages to weaken it with his weapon. Just as Noah attempts to leave, Clay messages him from the bridge. Clay sets the Ark to self-destruct as Noah escapes with Hayley.Noah and Hayley reach New Earth, but as they emerge from the escape pod Noah spots another human who turns out to be infected, and in the distance a huge monster. As the film ends, Noah raises his gun and utters "Burn 'em all".