The story begins with Rie at an underground drilling site. She is taking photos and asking questions of the crew. She is an artist/photographer/journalist doing a piece on the giant machines underground that society relies on.The workers are from all over, all speak different languages and have different backgrounds. Rie has a hard time connecting with them even though most of them speak English and they all have things in common like families and kids. She would like to go into the main drill and see how it works with an experienced worker, Vio and his helper Bharag. However, the foreman sees her inside and explains it is not safe, there are only two tanks oxygen so only two people should go. He does allow Rie to sit outside and watch via camera and through the window. She sees that the pressure inside the container is similar to being far under the ocean as Bharag shows her a water bottle squeezing under the pressure.While Vio is inside working on the cutterhead, which seems to be the main drill head, the foreman hears an alarm for carbon monoxide poisonous gas somewhere in the tunnel. A red light is blinking. Rie asks what is going on and the foreman explains he does not know. Finally above the machinery in the tunnel the Foreman sees smoke indicating a fire. He tells Rei to get inside the cutter's medical bay and he will turn on the oxygen. He also gives her a breather. He shuts the door, locking her in. Vio and Bharag are in the tiny compartment next to hers. She tries to explain she does not know what is going on.Some time passes in which we see Rie getting warmer and warmer in the industrial compartment. She starts to sweat and removes all non-essential clothing. She takes a look at the thermometer and it is 50C- very hot. She bangs on the window to the main compartment and yells through that she is very hot and needs to get out. She takes a piece of heavy equipment and manages to loosen the large screw holding the doors between the compartments sealed, and moves from the medical compartment into the main drill area with Vio and Bharag. They close the door behind her, so now all 3 are in the same small compartment. Vio explains if there was a fire it would explain the heat in the outer medical compartment. Rie asks how much oxygen Vio does not know and says the best thing to do is to calmly wait for help so as to save as much oxygen as possible.Some time passes in which we see them undressing, getting comfortable, maybe sleeping, looking bored. Bharag shares a sandwich with Rie. He tells her not to drink too much water and she asks why, prompting a conversation about Bharag being smuggled out of his home country, Eritrea, and how the smugglers would taint the water with gasoline to prevent people from drinking too much. Rie prompts Vio for action saying they cannot wait, how does anyone know they are there? What if they die waiting for help? Vio explains the pressure to get outside is too much, and opening the door would cause any fire to consume the last of their oxygen. He explains there is a medical supply area outside but it is too dangerous for any of them to go, and they are not even sure the supplies are still there, so it is better to wait. Rie's phone goes off- it is not a call though, it is an alarm that she is supposed to pick up her daughter from school. A conversation about their families passes between the three of them, with Rie admitting she had not even thought of her daughter, and Vio shaming her for not thinking of her kids. Vio insists they continue to wait for help even though they are all hot and breathing laboriously.Rie seems to accept his course of action but secretly doesn't. A short time later she claims she has to pee and says she will go into the medical bay to do so, asking for the door to be shut for privacy. What she really tries to do is shut the door between the compartments, effectively locking Vio and Bharag inside the main compartment, while she stays in the medical bay with a breathing filter. Before she can secure the door with the large clunky screw, Vio realizes what she is doing and pushes it open. He sees she was hiding a breather in the medical compartment the whole time, and sees that she had tried to lock them out.Suddenly the lights go out- we are not sure what happens, but we can assume that Vio and Rie are fighting over the breather. Eventually a flashlight is turned on. Vio has the breather and states that now he can get to the medical supplies outside and see if there are any left, yelling at Rie that she should have told them sooner there was a breather. They have a short debate on who should go out, with Bharag saying he needs to survive for his family, for money. He explains to Rie his family paid a lot of money to get him free and now they have nothing, so he needs to stay alive to pay them back. Rie asks how much and he says, too much. She repeats and he finally relents, $8,000. Rie says she has that and she can pay it for him when they get out. Rie doesn't seem to trust Vio and Bharag is also on edge about who should take the breather and try to make it to the supply closet, neither says anything but what if Vio just leaves them and does not return?Before Vio can do anything there is light outside the small window. A rescue crew has arrived. They say they will open the door from outside but before they do Vio says they must decompress the unit or they will all die. The crew says they will have to decompress from the inside because the machinery outside is broken. Vio begins the decompression.Before anything else can happen, there is an explosion outside and the rescue crew is gone, the window covered by smoke and debris. All three occupants of the drill go back into the main compartment but they cannot breathe and the decompression has taken its toll- Vio is struggling. Still they manage to open the door to the cutterhead, the small opening above the main compartment where the drill is located, an area no one is supposed to be in because it is so far underground there is no air and it is very unsafe. Rie crawls out, dragging Bharag with her, but Vio passes out inside the compartment and Rie leaves him there. She has the breather with her. She tries to rouse Bharag but he seems to have suffered the consequences of decompression as well and passes in and out. Rie says they need to dig their way around the cutter to the main tunnel. She frantically tries to do so, but every direction she digs she hits metal- it is useless. She lays down with Bharag and says they need to stay warm and stay together. The tunnel is now a mushy mess from water leaking down from above.Some time passes, in which Rie and Bharag share the breather, each taking a few breaths and then passing it back. Each time they pass the breather, they each struggle more. You can see the agony on their faces after each one finishes their breath, and they each claw and start to be more aggressive with the breather. This scene is extremely intense, you almost feel as if you are drowning and the breather is your only lifeline. Both become more and more desperate. Between breaths, Rie says "For your family," another breath, "the money", effectively saying in very few words that he should die and let her live so she can give his family the money. A struggle ensues- you cannot see much due to the flashlight dimming, but you see the mud slipping over the two as they both struggle for the breather. The struggle is tense and slow, highlighting their weakened state and lack of energy as they both slowly suffocate.Finally the scene settles, and you can see Bharag is on top of Rie with the breather. You cannot see Rie's face but it looks as if she is face-down in a puddle. Bharag has attempted to kill her so that he may survive. The scene fades to black.Moments later, light breaks through, and Rie's body is pulled from the tunnel. Bharag barely looks alive himself but opens his eyes when he sees the light.The scene then cuts to Bharag on a medical plane, with an oxygen mask around his face. He is clean and bandaged. He looks across from him to see Rie on the other side, laying down but breathing with a tube in her mouth. For a moment he does not seem sure she is alive, for a moment you wonder if he is going to try to kill her again so she does not tell what happened between them in the cutterhead. He stares at her body intensely. Finally he sees her breathing and sees her fingers move. He seems surprised. The camera pans out to where we can only see Rie as she opens her eyes, slowly comes to, and turns to see Bharag next to her. We do not get to see Bharag's face, only Ries' face, but the questions in her stare are obvious: what now? What would you do, if you had survived with another who had tried to kill you?