February 2049, three weeks after “the event” – a radioactive meltdown that has destroyed most of the world. Augustine Lofthouse (George Clooney) is a terminally ill scientist who stays behind at the Barbeau Observatory as all the other citizens are evacuating via helicopter, including a mother searching for her daughter – but the woman is told her daughter got on an earlier ride. Augustine lives alone at the facility, taking his medications, doing dialysis, and using the facility to see if any of the exploratory space missions looking for hospitable planets are still active. He finds that one mission, Aether, is still active.
The film flashes back decades earlier, where a young Augustine (Ethan Peck) presents his research on what other planets might be habitable for human life. After the presentation, Jean (Sophie Rundle) approaches him and asks him how much what he’s researching could be actually real. Meanwhile, one of the astronauts on the Aether mission, Sully (Felicity Jones), is pregnant and has a nightmare she’s been left on the planet that they were exploring, K-23. The others on the mission are Captain Gordon (David Oyelowo), Maya (Tiffany Boone), Sanchez (Demian Bechir), and Mitchell (Kyle Chandler). Sully tells the rest of them that she is unable yet to get any signal to communicate with Earth or anyone else.
At Barbeau, Augustine finds a young girl (Caoilinn Springall) hiding in the facility. He attempts to contact someone to come back to retrieve her but cannot get in contact with anyone. She doesn’t say a word, but when she draws a picture on a flower, he realizes her name is Iris. He explains to her that Aether is coming back and he needs to warn them about what has happened on Earth. The antenna is not strong enough and Augustine fails to communicate. Augustine tells Iris if she’s lost to always look at the star Polaris to find her way.
Gordon notes in his captain’s log that K-23 was a success, it could sustain life, but the inability to communicate with home – or anyone at all – is troubling. Meanwhile, in another flashback, Jean and Augustine are in a relationship but he is cold and only focused on his work, neglecting his own life. He barely reacts when she tells him she isn’t pregnant after a pregnancy scare, and she leaves him. In the present day, Augustine tells Iris there is one antenna that is stronger than the one at Barbeau since it is farther north and the air space might be clearer. He warns her it will be a long journey. He packs his dialysis machine and the two of them venture off into the brutal arctic cold to find the other station.
On the Aether mission, an alarm goes off alerting the team that they have gone off course, and all hands go on deck. They try to stop the drifting by plotting a course through an unmapped and uncleared zone territory, a dangerous and risky tactic.
Meanwhile, Augustine and Iris camp out overnight in the frozen tundra and the next day Augustine finds a downed aircraft, the pilot dead inside. He explores the hull and finds a man alive but dying. The man asks Augustine to execute him, and he does.
More flashbacks reveal that Jean did indeed have a daughter, who she raises alone. Augustine sees them and wants to know if she knows about him – Jean tells him if he wants their daughter to know about him he can introduce himself. On the Aether mission, Maya gives Sully an ultrasound, and Sully tells Gordon that they’re having a girl. Augustine and Sully find another space to spend the night, a trailer, and Augustine asks Iris to ask him a question, which she does – when he wakes and finds the trailer is filling with water. He manages to rescue Iris, but then the trailer and their vehicle sink into the ice, taking the dialysis machine with them.
They hide out in an ice cave and eat what little food they have remaining. They get caught in an icy wind storm that is essentially blinding, and Augustine loses Iris. He hears the sound of wolves and fires off a warning shot to scare them off. He calls out for Iris but cannot find her and collapses into the ground. He sees a vision of Jean appearing to him, but when he looks again it is Iris. He hugs her and they continue traveling, finally finding the other station.
In space, Mitchell congratulates Gordon on the baby girl, and tells him to name the baby Hyacinth after his mother – or “some kind of flower”. Sully finally begins getting a signal and begins communicating with Augustine at the new station. She asks for information on why they can’t communicate with NASA – Augustine begins telling Sully about what has happened to Earth when a red alert goes off – the ship is being pelted with meteorites, a consequence of them going through uncharted space. They make it through the meteor shower, but the ship has sustained damage and Sully has lost communications and radar.
The communications and radar damage means that one of the crew will need to do a spacewalk in order to fix it. Maya and Sully need to go, and Gordon accompanies them. The three begin making repairs on the outside of the ship. For inspiration, Sanchez plays “Sweet Caroline” through their headsets. They fix the radar and comms just as the ship is hit by more meteorites. They brace for impact and all manage to survive, but as they’re walking back into the ship Maya notices blood floating inside her helmet.
Gordon quickly gets her inside the airlock and are forced to wait for it to depressurize to help her while in the ship Sanchez races to get a medkit. When they finally do, they take her helmet off, and hundreds of drops of blood float out. Sanchez puts pressure on the wound while Sully tries to talk to her and keep her conscious, but Maya does not survive. The crew is devastated. There is a machine that plays memories of home for the crew, and Sanchez goes to it and plays Maya’s. As Mitchell pilots the shit and it approaches Earth, the crew finally sees that much of the Earth is smoking and destroyed.
Sully returns to the communications and radios back to Earth, where Augustine is dying without his dialysis machine. He tells them the only survivable areas are underground, and those are temporary. Most of the crew wants to go back to K-23, since Augustine has said Earth is unlivable, but Mitchell, who has a wife and kids, wants to go home. They receive a transmission from Mitchell’s wife just as the Earth was melting down saying that the kids are sick and she wants him to know where she’s going.
Mitchell tells Gordon he understands Gordon should go back to K-23 – Mitchell decides to take a re-entry pod to go to Earth to find his family. Sanchez tells him the pod needs two pilots and will go with him. Mitchell thinks he should stay – Sanchez tells him that his daughter died when he was four and he thought of Maya as a daughter to him and that he wants to take Maya home. Mitchell understands and agrees that they will go together. They say goodbye to Sully and Gordon and leave for Earth.
Sully makes a final communication to Augustine to thank him for what he’s done and how he’s one of the reasons she joined the space program, and that he worked with her mother, Jean. Augustine realizes she is his daughter – Sully says her named is Iris Sullivan – Sully for short. Flashbacks show that Iris is actually Jean and Augustine’s daughter. He tells her how nice it is to finally meet her. He asks her what K-23 is like, and she describes the planet to him. Augustine imagines being on the planet with Young Iris.
Sully speaks to Augustine but gets no response – perhaps he has finally succumbed to his illness – and she and Gordon realize its just the two of them and begin plotting a course for K-23.
