Inside a very dark pit, a man wakes up feeling rather disoriented. He has no memory of who he is or how he got here. After cracking his joints, he searches his pockets and finds a lighter plus some keys.
When he uses the lighter, he notices a wound in his arm. Then he looks around and is shocked to discover hundreds of dead bodies surrounding him. The horrifying view makes him throw up.
Suddenly lightning illuminates the area and the man notices Brown Eyes looking at him from above. The woman quickly disappears so the guy begins yelling for help while moving to the edge, which causes him to step onto a gun. At that moment Brown Eyes comes back and throws a long rope so he can climb out of the pit.
The man quickly gets out and begins searching the area until he finds a house with the lights on. He can hear people talking about him, apparently they aren’t sure if they should help him since he could be dangerous. The guy bursts into the room with his gun out and Lukas raises his shotgun in return.
When the man accuses him of being the killer, Lukas accuses him of the same thing. The man explains he doesn’t remember anything and that Brown Eyes helped him, so he wants to know why. The conversation is interrupted when Nathan falls to the floor as he screams and squirms in pain.
Sharon runs to his side and gives him some water to help him calm down. The man asks who all these people are, so Sharon explains none of them remembers who they are or how they got here, they only know their names because they had IDs, which Michael drops on the table. Unfortunately there’s no ID for the main guy or Brown Eyes.
Some of them have keys, yet they haven’t found any vehicles near the house. There are no phones or computers either. The man notices that Brown Eyes keeps writing stuff in Chinese but since nobody can’t understand it, he starts yelling questions at her.
The others stop him, pointing out that Brown Eyes is mute and doesn’t speak English. However they do have the feeling she knows them. They all woke up inside the house half an hour ago and she was already there.
Lukas thinks there’s something wrong with the main guy because he woke up in the pit while all the others woke up together and says he doesn’t trust him. Afterward the group explores the house. Sharon finds a locked door and tries her keys to no avail.
Lukas is looking around and notices wounds on his body. Brown Eyes tries to explain them with gestures, but Lukas doesn’t understand. Inside a pantry nameless guy finds a calendar with April 18th circled and he brings Brown Eyes over to ask if she did it.
She nods and again tries to gesture the explanation to no avail. Then Michael calls everyone over and shows them he’s found a closet full of weapons. He easily loads up a gun and Nathan guesses he’s a cop.
The man says they should all arm themselves and investigate the area, but Lukas convinces them it’s better to wait until morning. Moments later the main guy takes care of his wound and sees a quick memory of himself. When he finishes showering he hears the others saying that Brown Eyes has run away.
Lukas, Sharon, and the man go looking for her and as they search the woods, Sharon points out they aren’t near a city because the stars are too bright. As they walk around the main man sees a memory that shows him dragging a body with a seahorse tattoo, but he doesn’t say anything. Following a horrid smell, they discover a dead man tied to a tree with rope and wires.
At the house Nathan finds some books in Latin and realizes he can read them. He also recognizes them as medical and biological reference books. Michael keeps fooling around with weapons, saying his body remembers how to use them.
When Nathan finds a book in French and understands it too, Michael thinks this has to be Nathan’s house. In the forest, the trio keeps searching until they find an old shack. Inside they discover Brown Eyes feeding a tied woman.
When the woman notices the main guy, at first she hides and says “you used me”. Then she freaks out and tries attacking him while screaming about a daughter, so the man knocks her out by hitting her with his weapon. Lukas notices a camera on the ceiling with the light on, meaning someone is watching them.
After the group returns to the house, main guy is trying to open a mysterious door with some keys to no avail. Nathan talks to him in Latin and the man shocks himself by answering in the same language. Nathan feels a connection with the guy and Sharon, so he thinks he used to know them.
The main man tries ignoring him so Nathan explains that the door can’t be forced opened because it’s reinforced iron, then he decides to call the man John Doe. The next day the group is going out to look for cars. Michael says he should come along because he’s the best shooter, and to prove it, he tosses a mug and shoots it in the air.
However Lukas tells him to stay and guard the house. After they leave, a frustrated Michael tells Brown Eyes that protecting the group feels like it's supposed to be his job. Suddenly they hear a scream in the distance, so he sends Brown Eyes into the house before investigating.
It turns out there’s a man begging for help because he got stuck in a fence with barbed wire. When Michael gets close to help him, the man wraps the wire around Michael's neck to start choking him. As Michael struggles to breathe, the guy stabs him multiple times with a stick.
Meanwhile the group continues their search and sees the body again, assuming it could be a warning. Nathan’s throwing some rocks around and they hear one hit something metallic, so they follow the noise until they find two cars hidden under sticks and barbed wire. It takes a few tries, but Sharon manages to start one of the vehicles.
It doesn’t have much gas left, but they consider driving it anyway to see what they can find. At that moment Lukas finds a picture that shows every group member except for John, who points out he could be the one taking the photo. Lukas reminds them that they aren’t near anything so if they drive away they may run out of gas in the middle of nowhere.
Since the other car’s battery is dead, it’s better to return. On their way back they come across Brown Eyes, who immediately takes them to Michael. The group tries to save him, but unfortunately he ends up dying.
The trapped man starts screaming, so John shoots him dead. This causes him to see a memory of him smashing a woman’s head on the wall and dragging her body through the ground. As Brown Eyes has a breakdown, John takes Nathan’s keys and leaves with Sharon.
They push the car and get it to work so they take the road. Eventually they find an abandoned building with the number 18 on a wall and a truck in the garage. While looking at herself in the mirror, Sharon notices a kid running in the background.
They immediately go looking for him and hear him inside the building, but the front door is locked. When John starts asking questions, the kid calls him Jonah and tells him to go away because “they’re coming tomorrow”. At that moment a dog appears behind the door to furiously bark at Jonah.
He gets nervous and tells the kid to send the dog away, but instead the child threatens to order the dog to kill him. Sharon tries to calm them both down, however Jonah snaps and shoots the padlock, yet it doesn’t work. Next he starts hitting the padlock with his weapon, getting angrier by the second.
Sharon pulls him away and says this isn’t like him, which makes them realize they know each other. At the house, Lukas sees a memory of running through the forest while someone chased him. He also sees himself inside a cage while a man watched him, and another memory of Brown Eyes finding him outside.
In the present she’s touching his face and Lukas grabs her hand as he realizes he knows her. His grip tightens too much and Brown Eyes gets scared, so Nathan forces him to let go saying “stop it”. These words echo in Lukas’ head, making it hurt rather badly.
Minutes later Lukas is getting sicker and Nathan can’t figure out why. He asks Brown Eyes to take him back to the shack and Nathan realizes he knew this place. Unfortunately the prisoner has escaped.
Nathan remembers there’s a path around the lake and takes it to search for the missing woman. As he walks, flashbacks of him exploring this area come back to him. Eventually he finds a bunch of cabins and lots of bodies on the ground.
When he accidentally steps on some glasses, he recognizes them as his and puts them on. This triggers a memory of an argument with Sharon and Jonah about the inhuman treatment of certain people. Once he calms down he looks inside the cabins and finds a bunch of empty cages.
Suddenly he hears some crying and follows it until he finds the woman from the shack hugging her dead daughter inside a cage. He remembers her name is Helen and apologizes for the kid’s death, saying they’d been trying to help. A furious Helen tries to attack him, so Nathan rushes to close the cage and get out of the cabin.
After locking the front door too, he takes out his gun because he notices some people in a zombie-like state approaching him. Meanwhile Brown Eyes returns to the house and finds Lukas waiting for her. Feeling uncomfortable she immediately runs upstairs, only for Lukas to follow her because he doesn’t want to be alone.
Brown Eyes rushes to hide behind the iron door and Lukas begins banging on it, promising not to hurt her and claiming he remembers her. Since she won’t open, Lukas gives up and goes outside, where he finds a door that takes him into the basement. There’s a small lab down there filled with medical supplies, research, and a laptop.
Lukas turns it on and discovers the security cameras from the empty cabins. Next he finds a camera and watches a video of Jonah talking about an experiment on a person he found in the woods. He calls this “day 96”.
The captured person is Lukas, who is receiving a blood transfusion from Brown Eyes. Jonah says he’s made some progress and that the only side effect is memory loss. However Jonah gets angry when the transfusion’s effects don’t last permanently and the Lukas in the video wakes up, screaming in pain because of extreme headaches.
On the road Jonah and Sharon are making their way back when suddenly a tree falls in front of them. Jonah stops the car just in time and the duo hears a noise. They follow it until they find a bunch of people cutting down the trees.
When Jonah tries talking to them, the group screams and starts chasing after them with deadly intentions. Sharon falls as she runs so Jonah helps her up and together they return to the car. Since it won’t start, Jonah begins pushing it and the attackers catch up to him.
When they’re about to attack, the group sees two bodies hanging from the trees and immediately leaves. Jonah realizes the bodies were hung on purpose to keep people away, working as scarecrows. When the duo returns to the house Lukas is waiting for them with his weapon ready to shoot.
He tells Sharon what he saw and Jonah admits he’s remembered doing some bad things. As Lukas shows Sharon the video, he points out his wounds were caused by the needles and Sharon finds the same marks in her own arm. Jonah still doesn’t remember so Lukas knocks him out by hitting him with his gun.
Minutes later Jonah wakes up and finds himself being dragged by Lukas, who shoots at the ground to force him to fall in the pit. Among all the bodies he finds the seahorse tattoo and remembers hitting this woman, he also remembers Nathan telling him to “take it himself”. Another flashback shows Sharon, Michael, and Nathan afraid of him.
Lastly there’s a memory of Sharon asking him if he accidentally got blood in his mouth. In the house Lukas is desperate to leave and Sharon notices he’s having trouble remembering everyone’s names. Then Lukas grabs Brown Eyes in a very inappropriate way and when Sharon tries to stop him, he knocks her down.
Brown Eyes runs away and tries to hide behind the reinforced door, however Lukas catches up quickly and doesn’t let her lock it. He runs after her and Brown Eyes kicks him down, but Lukas recovers fast and grabs her to make her fall. Crawling on top of her, he kisses her by force.
At that moment Sharon fires a warning shot and Lukas jumps through the window to escape. Afterward Sharon goes to the lab and finds all the notes detailing the experiments, which triggers her memories. At the same time Brown Eyes uses rope to help Jonah get out of the pit again.
Then she draws the number 18 on the ground and points in the direction of the abandoned building. Jonah realizes they’re running out of time and makes her stay in the house while he investigates. Minutes later at the abandoned building, Jonah finds some tents and a picture of the kid with his family.
There’s a cage with blankets and a box that triggers a memory showing Jonah giving the box to someone and saying this is their last chance. Inside a different box he finds a map and another memory shows him telling the person to follow the road he’s marked. Suddenly he hears some noises and follows them into another room, where he finds two people in a zombified state.
The woman roars at him and causes him to drop the car keys, which she picks up and swallows. When she tries to attack him, Jonah shoots her dead. After retrieving the keys from her body, Jonah follows the map and finds the kid with his family trying to leave in their car.
An armed old lady knows his name and says he’s hurt them all, so she doesn’t want him near her loved ones. As the family leaves in the car, Jonah notices a sick teenager freaking out in the back seat. Afterward Jonah finds the box from his flashback which contains a bunch of vials.
This triggers a memory of Jonah cutting a brain open, followed by him telling the person with the box that the army will be waiting. The car from the memory has crashed nearby and the dead driver is still inside. Jonah carefully reaches inside and finds a map like his.
He also finds an important document with his name and a picture of him and Sharon that proves they're a couple. At that moment he hears a car and Jonah jumps out of the way before he gets crushed. The driver is Lukas, who looks incredibly sick.
Seeing him makes Jonah remember the day he caught him and he realizes he hasn’t been torturing people, he’s a doctor who has been studying infected humans to find a cure. He rushes to take a vial from the box but before he can give Lukas the injection, he’s pushed to the ground. Lukas grabs his neck to try to kill him, so Jonah reaches for a rock and smashes it on Lukas’ head.
As the man dies in Jonah’s arms, the rest of the memories come back. Jonah worked with Sharon, Michael, and Nathan. Lukas had been their first successful cured person and even thanked them for it.
But while they were celebrating this achievement, a woman escaped from her cage and attacked. Jonah defended himself and killed the zombie before blaming Nathan for not locking the cages well. Nathan claimed it wasn’t his fault and told Jonah to drag the body to the pit alone.
While Jonah was doing just that, the others contacted him on the radio saying that all the zombies escaped and were out of control. Jonah told them to inject themselves with the cure to survive, which explains the lack of memories. At that moment he was attacked by a zombie who bit his arm before pushing him into the pit, so Jonah injected himself too and passed out.
In the present Nathan returns to the house and hugs Sharon since now they remember they’re siblings. Suddenly two zombies appear at the door and break the glass to try to grab Nathan, but Sharon quickly shoots them down. Then they hide behind the furniture as they keep hearing screaming outside.
More zombies are coming, which means the scarecrows aren’t working anymore. The siblings open fire on any creature that gets too close to the door, but soon they run out of bullets. Losing all hope Sharon writes a note for Jonah, explaining they’re doctors searching for a cure for the zombie virus and that Brown Eyes is the key because she’s immune.
In the hidden room, Brown Eyes is terrified of all the screaming. At that moment they hear a helicopter and all the zombies are killed in seconds. This makes Nathan remember that the 18th was the day the rescue party would arrive.
He runs outside while yelling for help, however the soldiers surround him and shoot to kill him. At the same time Jonah arrives and is horrified to see Nathan’s death. Then he notices Sharon hiding nearby and runs to reunite with her.
They try running away only for a zombie to appear behind them and hurt Sharon. Jonah quickly shoots the creature and the noise gets the soldiers’ attention, so the couple runs to hide inside the pit. There both of them get an injection so they can pretend to be dead.
Before passing out, they kiss and Sharon gives Jonah the letter. While they sleep, the soldiers throw more bodies into the pit, including the child. Sometime later Jonah wakes up, but Sharon doesn’t because she’s dead.
He finds the gun but steps on the letter, so he doesn’t see it. Brown Eyes arrives and throws a rope to rescue him again. Together they cross the forest and find an even bigger pit with thousands of bodies.
