An emergency broadcast on TV announces the existence of a new virus that has appeared in an airport. Infected people become incredibly violent and soon the airport is on fire. Two months later the virus has spread around the world, becoming a global pandemic.
It transforms people into zombie-like beings called “ferals” and they’re seen as raging beasts. The government tries to establish a quarantine but many citizens protest against it and fight for the rights of the ferals, saying they’re people too. The army has to take over the streets and fight civilians to try to send them home, only to make the whole situation worse.
One afternoon, all TV channels lose their signals. Abigail and her brother get a call from their father the pilot, who explains he has lots of work to do helping people and promises they’ll be safe with their mother. At that moment they hear a noise from upstairs so the family runs out of the house.
When they’re about to get in the car, a feral jumps out and tackles the mother to kill her. Abigail immediately hides under the car and has to watch how the feral attacks her brother too. When a police siren starts wailing nearby, the feral runs away.
Afterward Abigail hears her brother call her name, but her mother transforms into a feral and finishes killing him. When Abigail cries, her mother hears her and goes after her, only to then get shot by Cassius. He rescues Abigail and she thanks him with a hug.
Her brother starts transforming too, so Cassius makes Abigail close her eyes before shooting the boy as well. Ten years later, the world is in a post-apocalyptic state. There aren’t many humans left and nature has taken over cities.
In the forest, a now teenager Abigail and Cassius are hunting. It’s clear that Cassius has trained Abigail well because she kills a deer with an excellently aimed shot, although Cassius scolds her for rushing and not being patient. When night falls the duo stops to camp and Cassius makes sure all the tripwires are in place.
A few hours after they fall asleep, one of the tripwires makes a noise and startles Cassius awake. He comes out of the tent to investigate and finds some fuzz stuck in the wire. Then he hears some noises nearby so he rushes to keep the horses calm and takes out his gun just in time to shoot an incoming feral.
This was probably a scout sent by the horde, so Cassius wakes Abigail to leave. For the next few days the duo keeps traveling and whenever they stop to let the horse rest, Cassius continues training Abigail. One afternoon they stop riding when they see a car nearby and quickly take their guns out.
They see a man shooting down a feral while a second creature approaches him from behind. Abigail wants to help him, but she shoots too quickly and the bullet hits him together with the incoming feral. The creature in the car comes out to eat and Cassius has to bring it down.
Afterward Abigail searches the car for supplies and Cassius finishes the poor man with a machete before taking his shoes. A radio in the car tries to contact the driver and Abigail wants to warn them about the feral horde in the area but Cassius tells her to ignore it. At that moment more cars show up and a group of survivors surround them with weapons.
They check the dead guy’s body and see a human killed him, so they assume the duo did it just to rob him. When the leader threatens to kill them, Cassius and Abigail attack the two nearest people and knock them down to steal their weapons. Things are tense as both sides point at each other, so a pregnant woman named Megan comes out of a car to try to calm them down.
At that moment the horses make some distressed noises and a feral horde appears around them. Everyone immediately opens fire, killing as many ferals as possible to try to keep them away. There are too many of them so they still manage to get close and Cassius and Abigail have to use their blades too, fighting them hand-to-hand.
However the other survivors are only good with guns so soon the ferals start killing them one by one. A woman gets a molotov bomb ready but is attacked by a feral, so it falls on a car and causes a small explosion that throws Cassius back. One of the survivors gets bitten so he tries to self-delete, but he’s run out of bullets and transforms instead.
The leader is grabbed by a particularly big feral and slowly beaten to death. Megan’s husband David is also tackled by a feral but he manages to kick it off. Abigail helps the couple get in a car and Cassius kills a few more creatures before joining them.
When they take off there’s a feral on the car roof, so Cassius stops the vehicle rather suddenly to make it fall. Abigail uses the chance to grab their things before they finally escape. The big feral notices that they killed his girlfriend and roars in fury.
Once they’re on the road, Abigail checks their ammo and notices they’ve lost most of it. Megan explains they were traveling to a colony on the riverside and that she’s in her 35th week, so the baby will be here soon. However Abigail and Cassius think searching for colonies isn’t worth it, they’ve already seen a bunch of them and they never survive.
Suddenly the car stops and the group discovers the engine is dead, so they have no choice but to continue on foot. Moments later the group makes it to an abandoned town and agrees to spend the night there. They search a building to make sure there aren’t ferals around and make camp.
Megan offers to share her food, but Cassius and Abigail only eat what they hunt to avoid the infection. The couple explains they talked to the colony on the radio, so they know they have plenty of supplies and doctors. It’s a week’s travel to reach it, meaning the risk is high.
In return Abigail tells them that she and Cassius are trying to get to the West Coast and escape to the islands by boat. After Cassius sets up the tripwires outside he takes out a map and tells the couple what path to take to reach the colony. However he refuses to go with them, saying the horde will come back for revenge.
Abigail talks to Cassius in private, insisting that they should help the couple and that maybe this colony will be different. An argument ensues yet Cassius still refuses to help. In the middle of the night the horde finds the broken car and follows the road to town.
Meanwhile the men can’t sleep so Cassius shows David that he always has a bullet saved in his pocket in case he’s bitten. The only thing David has is a cigarette and a twisted ankle. They chat for a while and end up bonding, so Cassius agrees to help them reach the colony.
The next morning Abigail hears a noise and goes downstairs to investigate. A feral suddenly attacks her and makes her drop her gun but Abigail can still kill him quickly with her machete. A second feral starts chasing her up the stairs and Abigail uses the broken window to throw the creature out of the building.
She almost falls too but Cassius catches her just in time. By the time the horde reaches the building the group is already gone. A feral trips on the wire and causes a small explosion that kills him.
Sometime later Abigail recognizes the area they’re in and remembers there’s a civil airport nearby where her father had a small plane. Cassius wants to keep moving and thinks an airport would make it easy for the horde to corner them, not to mention all planes are probably gone. However Abigail and the couple vote in favor of going there so Cassius has no choice but to follow them.
After walking for a while they find an old building and a car with a man that was shot recently. Cassius tells Abigail to check the building for supplies but refuses to actually stop to rest since he thinks they aren’t alone. Abigail only finds some coffee and doesn’t see the family hiding in one of the rooms.
Cassius checks the trunk of the car and finds a wheelchair, so they use it to transport Megan. After the group leaves, the horde finds the building and completely massacres the family in a matter of seconds. When they finally make it to the airport there are no planes around.
David and Cassius begin arguing about how to proceed but Abigail interrupts them when she finds her father’s hangar. Fortunately there’s a plane inside and David has the mechanical knowledge needed to fix it. While he works, Cassius and Abigail search the building.
Abigail finds a picture of her with her dad on the floor and puts it back on the wall. At that moment the horde arrives so the group rushes to get on the plane even though it isn’t ready yet. Cassius opens fire to slow the horde down and David moves the propeller manually to help the plane start.
Abigail’s knowledge of flying is vague and the plane is going slow, so the horde is getting too close. Thankfully she finds the right buttons soon and the plane begins gaining speed. A feral still manages to hang on the door and Cassius has to shoot it to make it fall.
Then the plane takes off and the group gets to escape. However they only fly around for a few moments before the plane starts failing and going down. Abigail tries to land it but the plane crashes against a bunch of trees and falls to the ground.
Luckily it lands on its wheels and everyone survives with just a few wounds. There’s a train station nearby so after making sure it’s empty they decide to rest there. Cassius opens the map and discovers it’ll take them two days to reach the colony, so they’ll leave first thing in the morning.
Abigail counts their ammo and notices there isn’t much left. Megan and Cassius share some food and Cassius admits she reminds him of his wife. He reveals he had to kill her infected family and that later she self-deleted because she couldn’t take it anymore.
Cassius also shares the story of a kid in his hometown who got bitten. Since the wound didn’t hit an artery, it took him a couple of days to totally transform. Meanwhile David finds a private spot to check on his ankle, revealing it’s not twisted.
The wound is actually a bite and David knows he should self-delete so he holds up the gun, but he can’t bring himself to do it. The next day the group keeps moving. As they walk under the strong sun David feels rather sick and Cassius notices blood on his leg.
He waits until the women are far ahead to push David against a tree and look at his ankle to confirm his suspicion. Cassius gives him the option to tell everyone on his own terms but if he doesn’t do it soon, he’ll shoot him. In the evening the group finds a house with the lights on.
When they come closer, a voice asks them what they want. Cassius thinks it’s too dangerous but Abigail approaches the house and explains they need help, swearing they mean no harm and mentioning the pregnant woman. Norton opens the door and holds them at gunpoint as he asks them to leave all their weapons in the chest outside.
Then he invites them inside, showing a very sweet and welcoming attitude. Cassius points out the house has power and Norton explains he’s an engineer, so he’s built a few devices that provide electricity and hot water. He also mentions a wife but ignores Megan when she asks where she is.
Norton shares his bread and vegetables with them and Abigail is happy to take a shower. Cassius can finally connect his laptop and look at old pictures, revealing his wife had been pregnant before the pandemic. When he checks on Megan, she admits she’s scared because she hasn’t felt the baby moving since they arrived at this house.
She makes Cassius promise that if something happens to her, he’ll protect her child. Afterward Norton shares a drink with everyone and explains he’s lived there for twenty years, but his wife isn’t around anymore. He’s heard about the colony on the radio but isn’t interested in joining them because he likes being alone.
Then Norton begins ranting about people being too obsessed with going back to the old ways and how humanity deserved the pandemic because they destroyed the planet and their ethics. He even compares the virus to evolution, saying only the strong people have survived. Cassius notices a strange knife on a table but Norton takes it away.
Feeling sicker by the second, David rushes to the bathroom and notices the infection spreading. When he comes out, he discovers his friends are unconscious because the drinks were spiked by Norton, who has put on a lab coat and is holding a strange machine. He can tell David is infected and activates the machine, which makes a noise that causes David to collapse in pain.
Norton explains the device is like a dog whistle that only works on the infected before David passes out. Meanwhile the horde has found the train station and continues their search. Moments later David wakes up to discover the whole group has been tied up in a basement.
Norton is there taking notes for his experiment and reveals that he’s got his infected wife locked up in a cage. He lets her out and controls her with his device to make her attack the group. Cassius and Abigail kick her a few times to keep her back so the woman goes after David, who manages to break the ropes to fight back.
They only struggle for a few seconds before David overpowers her, and Norton has to use his machine to stop him from rescuing the others. However David isn’t completely transformed yet so he’s able to push through the pain and break the rest of the ropes. Cassius finds a gun and tries shooting Norton, who immediately runs away.
The group rushes upstairs and locks the door behind them, so Norton starts hitting it with an axe. Abigail steals Norton’s car keys and Cassius retrieves their things before punching David. He wants to shoot him now but the women convince him to wait.
On their way to the car, Megan discovers that her water has broken. Norton comes out to watch the group drive away while his wife growls at him. When the car reaches the forest, the horde finally finds them and chases after them.
The group can see lights in the distance, which means they’ve found the colony. They try driving as fast as possible but unfortunately the road is blocked by a tree and they must continue on foot. The horde is getting closer so they open fire, but David runs out of ammo.
Since he’ll transform soon anyway, he tells the others to go while he buys them some time. The couple shares a heartfelt goodbye and before the trio leaves, Cassius gives David his bullet. Once they’re far enough, David smokes his cigarette and starts fighting the ferals hand-to-hand.
He manages to defeat a few of them but the big feral surprises him from behind and breaks his neck. The rest of the ferals chase after the other survivors so Abigail has to open fire to protect Cassius as he carries Megan. She also starts yelling for help and gets the attention of the guards at the colony gate, who quickly shoot all the ferals chasing after the trio.
When the rest of the horde sees the bodies and the lights, they immediately go back to the forest. Afterward the heroes are allowed into the colony and Megan is taken to the infirmary where a midwife takes care of her. The next morning after meeting the colony leader, Cassius tells Abigail that they should leave soon because humans can’t be trusted.
However Abigail is tired of running and ignores him. Then Cassius talks to the midwife, who tells him the baby is fine but the mother only has a few hours left. Cassius visits his friend and learns that the baby is a girl named Hope.
Megan reminds him of his promise and gifts him her family locket before finally dying. Meanwhile Norton arrives at the forest and finds all the bodies. Wandering around allows him to see the colony too.
At that moment the horde tries to attack him, but he immediately controls them with his device and announces it’s time for revenge. Back in the colony, Cassius is taking care of Hope and wondering what to do next. Abigail bonds with the local teenagers and joins a little party in the evening.
Alcohol is passed around and two guards fall asleep, so a few teens use the chance to enter a tunnel. Abigail follows them and discovers a strange remote control, but when she touches it Roderick stops her. He explains that the entire boat town is mined and the remote will blow it up if the ferals manage to invade it.
Humans can be safe from this explosion by using a hatch on the ground that will take them to an abandoned dam. The next morning Norton sees a guard on a boat and asks for his help. After getting rid of him, a feral jumps into the water and climbs into the colony to kill the other guard too.
Now Norton can send out the entire horde to attack. As survivors are killed all over the place, a few armed people come out to fight. Abigail saves Roderick from a feral before assigning tasks to the teen gang: those with weapons must find a higher position to open fire and Roderick must guide survivors to the dam while she goes looking for Cassius.
As panic takes over the colony, the midwife takes Hope from Cassius so he can search for Abigail. The people with guns are starting to run out of ammo and the colony leader tries to run away, but a feral immediately kills him. Abigail shoots a feral that almost kills two young girls while Cassius stabs a creature to save two teenagers.
Then Abigail and Cassius finally reunite and start fighting the ferals together using a combination of guns and hand-to-hand combat. When they see an opening they try to join the evacuation, but Cassius gets distracted when he sees Norton and a feral tackles him down. Cassius manages to stab the creature only to be found by Norton, who starts kicking him while talking about making a safer world.
After some struggle Cassius manages to stand up and pushes Norton against a wall to smash the device over and over until it’s broken. Then Cassius runs back to Abigail while the ferals jump on Norton to kill him. The survivors finish crossing the tunnel and make it to the dam so they ask Roderick to activate the explosives, but he hesitates because Abigail isn’t out yet.
In the colony, the big feral tries attacking Abigail so Cassius hits him with an oar. When the creature falls, Abigail notices his bracelet and is horrified to realize this is her father. The shock leaves her frozen so Cassius has to snap her out of it and drag her to the hatch.
The duo gets in the tunnel right before Roderick gets tired of waiting and blows the place up, killing every single feral in the colony. Afterward the survivors discover an infected man among them. As Cassius tries to calm him down, a feral jumps out of nowhere and kills the guy.
Then it turns to attack Cassius, triggering a fight. They continuously hit each other until they fall to the ground, where the feral almost bites Cassius. This time Abigail is patient and waits for the right moment to shoot, killing the creature without hurting her friend.
The survivors watch the colony burn and wonder what to do next. Abigail tells them they can build a new home in the dam and Cassius reveals he stole Norton’s notebook with the instructions to build a generator.