NOTE: This spoiler was submitted by Spectre

We open to title cards explaining that the International Space Station or I.S.S. was created after the Cold War by the United States and the Russian government as a means of collaboration between the two nations. Their mission together is primarily research for the greater good. To travel to the station, the Soyuz rocket is used.

Soyuz Rocket, Present Day.

Two astronauts Dr. Kira Foster (Ariana DeBose) and Christian Campbell (John Gallagher Jr.) are traveling to the I.S.S. Over their comms, they are congratulated for now being real astronauts. As they are docking with the station, Campbell explains that the Russians knock three times to tell the others it is okay. He also notes he has daughters, and one is not speaking to him much, being a teenager.

Kira and Campbell get inside the station, the former getting a hero’s welcome from the others as it is her first day; her commanding officer Gordon Barrett (Chris Messina), Weronika “Nika” Vetrov (Masha Mashkova) and brothers Nicholai Pulov (Costa Ronin) and Alexey Pulov (Pilou Asbæk), who round out the Russian crew. They all pose for a picture on the camera screen.

Kira talks with Nika and Kira notes with awe that Nika has been there for fifty days. Nika tells her the most important thing up there is that they stick together.

Kira meets with Gordon, who gives her a short tour, shows her where her stuff is stored, and her sleeping quarters. He mentions that learning to sleep will be a struggle initially; some sleep strapped in a bag, while others have learned to free float in their quarters. He advises her to use a sleeping bag until she is comfortable.

Gordon tells her video chat is available if she would like to speak to someone from home. Kira quietly deflects, saying she doesn’t have anyone to call.

Gordon points out the hum they all hear and explains that it is the life support system. If they don’t hear anything they are in serious trouble.

Gordon shows her work station, and the lock boxes to secure their research. Kira says she is ready to get started on her work and does so, bringing out several mice to put into a cage and observe for her experiments. During this time, she meets Alexey and he notes they will be working together in close proximity for a while. Kira notes she has read his papers and asks about the results of the experiments they have done so far. Alexey notes they have not ended well, meaning many dead mice.

Later, Kira hangs with the crew, watching Christian experiment with a drill that can spray fire. She watches as Nicholai exercises.

Later, the crew talks and has dinner together, Gordon telling Nika he wants to see Siberia. On the speakers, “Winds of Change” plays and Gordon makes a bad joke, which makes Alexey mad as the song means a lot to him when he was growing up. The tension is ultimately defused. Christian gives the groups gifts; candy, a drawing from Nika’s nieces, and a necklace made from space tether for Kira. Nicholai produces a bottle of alcohol and as he is about to explain the proper way to open it, Kira accidentally tries to open it normally, causing bubbles of alcohol to float in the area to the laughter of both crews.

Kira is told they want to give her a tour of the viewing deck. Christian says they don’t have much to be excited about and showing her this counts as something. Kira agrees and is led up to a chamber with a large window that allows her to see the entire Earth. Kira is amazed but somewhat stoic as the others speak of the outsider effect, and that she is one of only 500 people to have a view of the world like this. Kira cannot help but smile.

Later that night, Kira tries to sleep but is restless in the bag. As she is about to leave her quarters, she is spooked by Nika. Nika helps her back into the bag and secures her in. Nika notes that one of the negatives of space is the lack of “being held” and other intimacy.

The next morning, Kira and the others get up and attend to their duties. Christian notes the computers are down so they cannot get messages out.

Kira checks on the mice to see they have attacked each other. She is shocked and wonders why.

Going up to the viewing deck, Kira is shocked to see what appear to be several eruptions across Earth. After a few moments, it becomes apparent that this is not an isolated incident. Explosions are occurring everywhere on Earth.

Both crews begin to panic and call for help from their respective mission control. Christian is thinking of his daughters, while Nika thinks of her nieces.

Nika goes to speak to Alexey, seemingly conspiratorially, only to tell him she hid a bottle of Vodka underneath one of the consoles.

Gordon is at the computer when a message from mission control finally comes through, for his eyes only. He learns the United States and Russia are at war, with the involvement of other countries to be determined. Nicholai is at his station, getting orders from his government. Gordon gets his final directive; he is to take the station from the Russians. BY ANY MEANS NECESSARY. Gordon can only ask himself why, and hides the orders from Kira and Christian momentarily. Around that time, the station powers down unexpectedly, before resetting.

When they get a moment alone, Kira and Christian learn the truth and are horrified. Christian quickly deduces that the Russians probably got similar orders as well. Nika comes up to them, telling them they have a big problem. It turns out the station has lost its propulsion and is falling out of orbit. They have a day before the entire site will burn up in the atmosphere. Without getting a message through to get a boost in propulsion, the six of them will be dead within a day. Someone suggests the Soyuz rocket but there isn’t enough room for everyone and they are not to the point of making that decision yet. Kira sends out a message, requesting propulsion, hoping mission control will get it.

Gordon is told that an antenna outside the station is damaged, and needs to be repaired. Though suspicious, he volunteers to go out and fix it. Gordon suits up while Christian quietly voices his concerns. Nika comes up to Gordon and double checks his suit and kisses him deeply, revealing the two are lovers. Gordon tries to assure Kira and Christian. “I trust Weronika, I trust all of them,” Gordon says.

Gordon goes outside the station into space. As he gets his bearings, he sees the Earth is now the color of bright red, meaning massive parts of the world, including the United States, have been outright destroyed. Talking to Kira on comms, he orders her to keep EVERYONE away from the windows. Seeing the reality of their situation could crack their already fragile bond they have.

Christian and Alexey talk, the latter talking about CO2 poison and a headache he is getting. Christian is tense and paranoid. As it turns out he is rightly so.

As Gordon travels to the antenna, Kira asks him about Nika. After some prodding, he mentions he never knew her before the station, and fell for her after a night of bad karaoke.

Alexey opens a panel and stares at a bunch of wires. He goes to cut one but hesitates.

In turn, Gordon asks Kira about her life; how she went from a biologist, to the Marine Corps, to being an astronaut. Kira says she spent seven years working with her girlfriend/fiancé and her best friend on organ replacement science, having lost her father years before waiting on a donor. Kira says she no longer has her fiancé as the fiancé and her best friend got together behind her back, breaking her heart. “Trust isn’t my strong suit,” Kira notes. She is alone, and has buried herself in her work to cope.

Alexey cuts the wire. That cuts the communication between Kira and Gordon.

Gordon is almost at the antenna but cannot communicate with Kira. He realizes he cannot reach the next section without removing himself from his tether. He unlatches and makes a leap of faith. Gordon notices that a grabber arm is moving and tries to communicate that he doesn’t need it. When he gets to the antenna he sees that it is perfectly fine. He realizes it was a trap and the Russians set him up. The grabber arm twirls in a circle, and swats him off the station, seemingly killing him. We see that Nicholai was controlling it, having also gotten orders to take the station by any means necessary.

Not being able to contact Gordon, nor see him outside, Kira and Nika begin to panic. They suit up to see if he is still connected to his tether and are horrified to see that he is not. Both Kira and Nika want to go out and find Gordon but their respective crew members tell them Gordon is dead.

Nika confronts Alexey and Nicholai and learns the truth about what happened. Heartbroken and horrified, she vows to tell the others what they did. “No one deserves what you did to Gordon. No one,” Nika says.

Nika breaks down, sobbing at the loss of Gordon.

Christian pulls Kira aside and tells her that it is obvious that what happened to Gordon was no accident, and he needs to be sure she is with him. Kira asks if what truly happened wasn’t an accident. What should they do?

Nika tells Kira she needs to speak to her alone, saying she needs her help. Nika wants Kira’s lockbox key and will give hers in exchange. Kira claims to have lost it, and Nika scoffs. As she goes to leave, Kira tells her the truth; that they got orders to take the station too. Nika, satisfied, tells her to raid Alexey’s box, which contains samples that could be used to treat radiation poisoning. Whatever nation takes over the station will have the research and will use the potential power of saving life as the ultimate bargaining chip. Nika wants lives to be saved, so she tells Kira to take the samples and leave in the Soyuz rocket. Nika will cause a distraction to buy time until they can be rescued. “I’m helping you because you told the truth. Your job is more important,” Nika says.

The two trade keys. Nika tells Kira to work fast.

Nika grabs the drill/fire gun and turns on pure oxygen in one of the chambers. Nicholai and Alexey confront her. Angry over losing Gordon and horrified at how they went from friends to monsters, she wants to end things quickly by using the drill to spark the oxygen. The three are caught in a standoff.

Kira goes to the research lab with Christian. Saying she is looking for the Zero Node, Christian tells her there is no such thing. Kira believes Nika lied to her and goes to find her.

As Alexey and Nicholai try to talk Nika down, Kira and Christian sneak up behind her. Having little choice, Christian smashes a tank in the back of her head, killing her. Alexey and Nicholai are devastated as Christian tries to tell them he had no choice.

Alexey and Nicholai mourn Nika. Kira tries to deny her death, but Christian knows he caved her skull in with the hit. He tells Kira he just wants to go home to his kids.

Nicholai tells his brother that he is finishing it. Alexey asks him what he means. “You know what I mean,” Nicholai intones. Nicholai tells his brother that the Americans killed their friend. “WE KILLED OUR FRIEND!” Alexey screams. Nicholai tells him he is a good son and a good brother. He leaves him to track down and kill Kira and Christian. Alexey screams his brother’s name and mourns Nika.

We see more shots of the world in flames.

Alexey finds the bottle Nika hid and drinks heavily. Looking at the monitor, he calls out Gordon’s name. He is still alive. Using the grabber arm, he is able to bring him back inside.

Kira and Christian hide in the luggage from Nicolai. Kira tries to evade him only to be seen by Alexey, who pulls her to the side. Nicholai calls out to Kira and Christian, lying that Nika is just injured and can be healed and they should try and work things out. Finding Christian, Nicholai attacks him only to be stopped by Gordon, who asks where Nika is.

Realizing she is dead, the enraged Gordon fights Nicholai in a locked hallway. Attacking Nicholai with a drill, Gordon grapples with him, only to get the drill taken from him. Nicholai impales Gordon with the drill. Gordon, with the last of his strength, grabs a screwdriver that Nicholai had and pierces his neck in turn. Both die, their bodies floating in the hallway. Alexey, Christian, Kira, who had tried to stop them, forced the door open too late.

The remaining three bundle up their dead friends in sleeping bags and mourn them. They then proceed to mourn privately.

The world continues to burn.

Looking around the station, Kira notices a sign that says NODE ZERO. Realizing Nika was telling the truth about the samples, Kira goes to Christian’s quarters to tell him, only to find the samples and a Soyuz suit. Christian knew about them all along and is now planning to sell them out.

The life support ventilation goes out.

Kira finds Christian and Alexey making food. Christian is tense, waving around a knife and reveals Nika told her to leave them behind with the samples, but claims to have forgiven her. He does note that some of them will become heroes despite this horrific incident. Kira realizes that Christian has gone mad, perhaps realizing his family is dead, and having nothing else, wants to escape the station the only way he knows how. She points to Alexey, who turns off the music that was playing, and he realizes the life support is off.

Kira pretends to make a sandwich. She taps a condiment bottle three times to tell Alexey subtly that she is on his side. Kira asks to use Christian’s knife, which he initially refuses, before being okay with it, owing it to CO2 sickness. Christian asks to talk to Kira alone. As Alexey goes to leave, Kira tells him in Russian something Nika once said; that the most important thing is they stick together. Christian once again asks Alexey to leave. Kira repeats the statement. Realizing he is found out, Christian admits he disabled the life support but he can reverse it. “So can I,” Alexey replies.

Grabbing the knife, Christian stabs Alexey through the hand. Despite the pain, Alexey grabs him tight, while Kira uses the necklace Christian gave her as a garrote, choking him to death. It takes several moments, but Christian dies, as the two remaining astronauts float with his dead body, devastated.

Kira bandages up Alexey’s stab wound. As they sit in the viewing chamber, the message request for a propulsion boost is seen and acknowledged, getting them out of immediate danger.

Communications on both sides return, with their respective governments asking if they have taken control of the station. Angry and disillusioned by their selfish governments, the two ignore the messages and use the Soyuz rocket to leave the station with Alexey’s research. As they leave the station, plummeting into free fall back to Earth, Alexey asks a pertinent question, given that most of the world has apparently been destroyed and their respective governments are at the precipice of collapse.

“Where are we going?” Alexey asks.

“I don’t know,” Kira replies.

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On the International Space Station, six astronauts, three American, three Russian have their peaceful research interrupted when the world falls into nuclear conflict. Getting messages from their respective governments, they are told to take the station over by any means necessary.

Nicholai (Costa Ronin) makes the first move, seemingly killing Gordon (Chris Messina) by pushing him off the station while he is outside making a repair. Weronika "Nika" Vetrov (Masha Mashkova), Gordon's lover, tells Dr. Kira Foster (Ariana DeBose) to take the research the Russians were doing on radiation therapy off the station while she makes a distraction. Instead, horrified by her comrades' actions, Nika plans to commit a murder/suicide, blowing up the station. Christian (John Gallagher Jr.) is ultimately forced to kill her by caving in her skull.

Nicholai tells his brother Alexey (Pilou Asbæk) that he plans to finish the takeover and kill Kira and Christian. Alexey sees Gordon is still alive and rescues him. When Gordon finds out Nika is dead, he and Nicholai fight, the two killing each other.

Soon after, Kira discovers the samples she tried to recover do actually exist, despite Christian denying they did. It turns out Christian knew they had but having gone insane by the destruction of Earth and most likely his family, has chosen to escape alone. Kira and Alexey team up and reluctantly kill Christian when he tries to stab them.

Communication with their respective mission control resumes, each asking if the other finished taking over the station. Angry and disillusioned, Kira and Alexey refuse to neither answer nor comply. Instead they take the Soyuz rocket with Alexey's research and free fall back to Earth. With most of the Earth destroyed and their government's in chaos, Alexey asks where they are going. Kira says she does not know.