2079. Washington, D.C.
CIA agent Snow (Guy Pearce) is captured by Secret Service director Scott Langral (Peter Stormare), who has security footage of Snow killing infiltrated CIA agent Frank Armstrong, who was investigating a mole that is selling governmental secrets. Snow claims he's innocent, and later directs his friend, CIA agent Harry Shaw (Lennie James), to find Snow's contact and friend, Mace (Tim Plester), and find the location of a briefcase containing the information that Armstrong had acquired about the mole.
Meanwhile, Emilie Warnock (Maggie Grace), daughter of President Warnock (Peter Hudson), travels to M.S. One, a maximum security penitentiary in Space, where convicts are kept in suspended animation, to investigate claims that the stasis might affect prisoners' minds, leading to psychopathy and dementia, and that they're being experimented on by the government. One of the prisoners, Hydell (Joseph Gilgun), is awakened so Emilie can interrogate him, but he steals a gun from Emilie's bodyguard, Hock (Jacky Ido), and escapes. Hydell releases all the prisoners and starts a riot, led by his brother Alex (Vincent Regan). Emilie and her associates are captured, and Alex decides to kill one of them to prove their point. Hydell quickly kills the warden before he is able to tell Alex something important, and Alex begins to grow impatient with Hydell's excessive sadism.
Hydell destroys all the ships aboard M.S. One against Alex's orders, preventing the Secret Service from sending a team to rescue the hostages. Langral then decides to send Snow alone to rescue Emilie, and leave with her in an emergency shuttle on Level 3. Snow is initially reluctant, but accepts the mission after Shaw tells him that Mace is in M.S. One, and could help Snow prove his innocence. Snow heads there, hidden in a spaceship transporting a hostage negotiator.
During their meeting, the negotiator, knowing that Emilie has a wounded leg, attempts to convince Alex to release an injured female hostage as a sign of good will. Alex agrees to surrender Emilie, but Hydell shoots Emilie's friend Kathryn (Anne-Solenne Hatte), so Alex is forced to deliver her instead. Realizing Hydell has become obsessed with Emilie, Langral tells Snow to infiltrate the prison, but he's spotted by Alex's men. Realizing what has happened, Alex kills the negotiator. He soon realizes that Emilie is the President's daughter, and decides to isolate her from Hydell, but she manages to escape with Hock's help and they hide in a storage room, damaging the electronic lock in order to prevent Alex's men from reaching them. However, this causes their oxygen supply to slowly run out. Hock sacrifices himself in order to leave more air for Emilie.
Snow is guided by Shaw through the air ducts, and manages to enter the storage room and rescue Emilie before Alex's men break down the door. Realizing Snow is being guided, Alex cuts his communication link with Shaw. Meanwhile, Snow takes Emilie to the medical bay, where he treats her wounds and changes her appearance so they can blend in with the other prisoners. They quickly find Mace, but learn that the statis has caused dementia. Their cover is blown by Alex, who reveals that Emilie is the President's daughter and orders the convicts to capture them.
Snow, Emilie and Mace attempt to reach the escape pod through the inferior levels, but a satellite crashes against M.S. One, separating Mace from them. He utters the words "Lullaby" and "I see you, I foresee you" to Snow before the room he's in depressurizes, killing him. Although Emilie claims she knows the briefcase's location and promises to lead Snow there if he helps her rescue the hostages, Snow takes her to Level 3, only to learn that the pod only has one seat. Realizing he was sent there to die, Snow sends Emilie on her way and stays behind, but she climbs out of the ship before it departs. Unbeknownst to them, the crash has shifted M.S. One out of its orbit, and it'll soon enter Earth's atmosphere, where all inside will be burned alive in re-entry.
Hydell approaches Emilie through the comms and requests that she reveals her location in exchange for the hostages' lives. She tells him she's in Level 3, but he murders the hostages anyway, forcing Snow and Emilie to run to another part of the station in order to escape from him. They discover a second medical bay where the prisoners were being illegally used as test subjects. Alex finds them there and captures Emilie after overpowering Snow and leaving him for dead. Upon learning Hydell has killed all the hostages, Alex beats him and contacts the President, threatening to allow Hydell to rape Emilie if they're not released. However, Langral relieves the President of his duties by claiming he's emotionally compromised and orders an air strike to destroy M.S. One.
Hydell prepares to rape Emilie, but Alex stops him. Infuriated, Hydell stabs Alex dead. He returns to Emilie, but Snow stops him and escapes with Emilie as Hydell and the others chase them. Meanwhile, a bomb is planted on M.S. One. With Shaw's guidance, Snow and Emilie find skydiving suits and jump out of M.S. One as the bomb explodes, killing Hydell and all the others.
The suits allow Snow and Emilie to re-enter Earth's atmosphere and parachute to safety in New York City. Emilie is taken to the hospital, while Snow is arrested. At her bed, Emily realizes Mace had actually given them the code "ICUI4CU", which opens the briefcase, hidden in a locker in a subway station with the word "Lullaby" spray painted on it. Emilie then finds evidence that the footage of Snow killing Armstrong was forged and delivers the briefcase to Shaw during a meeting with Snow. Shaw opens it, but finds nothing, then realizes that Emilie hadn't told him the code. Realizing Shaw is the mole, Langral arrests him and releases Snow.
Snow retrieves the lighter that Armstrong had given him before dying, only to realize that the microchip with the true evidence and the secrets that Shaw had stolen are hidden inside. Snow decides to keep it for himself in case he needs to use it as leverage, and is then approached by Emilie, who has learned his first name is Marion. She thanks him for saving her life and they begin a romantic relationship.