The Avalon, a sleeper ship transporting 5,000 colonists and 258 crew members in hibernation pods, is traveling from Earth to the planet Homestead II, a 120-year journey. After only 30 years, an asteroid collision damages the ship (although theoretically it is damage-proof), resulting in a malfunction that awakens mechanical engineer James "Jim" Preston, 90 years too early. After a year of isolation, with only an android barman named Arthur for company, Jim grows despondent and contemplates suicide until noticing Aurora Lane, a beautiful young woman inside her pod. Jim views Aurora's video file and is smitten. He struggles with the morality of prematurely reviving her for companionship for quite some time; knowing doing so will rob her of a future life. Jim eventually does awaken her and lets her believe her pod also malfunctioned. Jim asks Arthur to keep the secret of what he has done. Aurora, devastated at having to live out her life on the ship, unsuccessfully tries to re-enter hibernation. Resigned to the situation, Aurora, a writer and journalist, resumes writing about her experience. Jim and Aurora slowly grow closer over the next year, eventually falling in love. Jim intends to propose to her, but Arthur inadvertently reveals the truth when he hears Jim say there are "no secrets" between Aurora and him. Aurora berates, shuns, and even physically attacks Jim. She furiously rejects his apologies and avoids contact with him. Sometime after, another pod failure awakens Gus Mancuso; deck chief officer. He discovers multiple failures throughout the ship's systems, despite the computer not revealing their origin. If not repaired, the mission may fail which would kill all the hibernating passengers and crew. Gus attempts to repair it with Jim and Aurora's help, but he falls critically ill. The Autodoc, the automated medical diagnostics and treatment pod, reveals that Gus has suffered a pansystemic necrosis caused by multiple failures of his hibernation pod, and he has only hours to live. Before dying, Gus gives them his deck chief ID, allowing them to access crew-only areas and try to repair the ship. Jim and Aurora discover a series of hull breaches from the asteroid collision two years earlier. The computer module administering the fusion reactor powering the ship is critically damaged, causing the ship's cascading malfunctions, as the other systems divert computing power towards trying to maintain the reactor. Jim and Aurora replace the damaged module, but when the computer attempts to vent the reactor to extinguish a runaway plasma reaction, the exterior vent hatch fails. Jim is forced to spacewalk and vent the plasma from outside using the manual hatch controls within the vent tube.A malfunction forces Jim to stay within the tube to manually keep the hatch open, while Aurora initiates the venting from inside the ship. She admits being terrified of losing him (whom she still dearly loves) and being left alone as a result. Jim uses a door as a shield, but is blasted out into space and his tether snaps on top of his damaged spacesuit rapidly losing oxygen. Aurora retrieves a clinically dead Jim from space and manages to resuscitate him in the Autodoc while the Avalon, its reactor repaired, returns to normal operations.Afterwards, Jim learns that with Gus' clearance, the Autodoc can function as a makeshift hibernation pod for one person. He offers to put Aurora back in hibernation for the remainder of the voyage. This gives her the chance to live her desired life on Homestead II; with Jim willing to become alone again. Realizing that she would never see Jim again on top of finally understanding of what Jim was going through when he decided to wake her up, Aurora chooses to remain awake with Jim. He presents her with the ring he made earlier, which she accepts.Eighty-eight years later, the ship's crew is awakened on schedule, shortly before arrival at Homestead II. In the ship's grand concourse area, they discover a huge tree, many trailing vines, much vegetation, birds flying, and a cabin. Aurora's voice-over is reading her story, describing the wonderful life she and Jim had together on the Avalon.