In 1968, two epidemiologists appear on a tv show explaining their worries for the future. One of
them is worried about newfound viruses traveling around the world because of planes, but the other
one thinks humanity always beats viruses and that they should worry more about fungi. Right now
fungi don't sound like a big deal because they're only capable of controlling animals, but if
climate change keeps affecting the temperature of our planet, fungi could evolve to the point where
they could control humans as well. Unfortunately neither the host nor the other epidemiologist
takes him seriously. In 2003, Sarah begins her day making breakfast as a birthday present for
her father Joel, and her uncle Tommy joins them as well. While they eat, they hear on the radio that
there have been some disturbances in Indonesia. Before leaving for school, Sarah secretly searches
Joel's drawers to take his broken watch and some money to fix it, although she can't help
but be curious about a knife her dad has hidden as well. When their family leaves the house,
they find their neighbor Danny taking care of his Nana, who lives in a catatonic state in her
wheelchair. Danny tells them they haven't visited in a while, so Joel makes up an excuse about being
busy but promises Sarah will come by later. Later after class, Sarah goes downtown to get Joel's
watch fixed. While the clocksmith is working on the watch, his wife suddenly shows up looking
quite scared and closes the shop four hours later. The clocksmith doesn't understand what's going on
but he hurries to finish his work so Sarah can leave. Afterward, Sarah visits her neighbors,
and Danny's wife Connie shares some cookies while Sarah pets the dog Mercy. Sarah comments that she
saw lots of police and trouble on the road on her way here, but Connie hasn't heard anything
on the news. The house has a big DVD collection and Sarah is so busy browsing it that she doesn't
notice Nana having a strange kind of seizure even if she isn't supposed to be able to move.
Sarah chooses one of the movies to borrow, and on her way out, she notices Mercy staring at
Nana curiously. When she goes home, Sarah notices a bunch of army planes flying really low over the
town. Later she hears on tv that there has been a rash of violent incidents across the city, but the
police blame it on a new illegal upper hitting the streets. The tv is quickly turned off when Joel
comes home and Sarah gives him the fixed clock as a birthday present. The movie she borrowed
from Connie is also one of Joel's favorites, so they decide to watch it together as part
of the birthday celebration, although Sarah falls asleep. Out of a sudden, Tommy calls Joel to ask
him to bail him out of jail. He got arrested when he was in a bar and some guy suddenly went crazy,
starting a fight just because. Joel puts Sarah in bed and leaves in his truck. Three hours later,
Sarah wakes up when she hears lots of noises outside: helicopters, screaming, and general
disturbances. She leaves the bedroom and when she can't find her dad, she turns on the tv, only to
find a "national alert" signal telling citizens to stay indoors. Suddenly a thud at the window
startles Sarah: it's Mercy, who is incredibly scared. Sarah goes outside to calm him and tries
to take him home, but Mercy whines and struggles against her hold until he frees himself from the
collar and runs away. Not understanding why the dog would hate his own home, Sarah goes to check
on the neighbors and finds the door open. She enters the house, and because all lights are out,
Sarah doesn't notice the blood on the floor until she steps on it. The blood trail comes from Danny,
who is wounded on the floor and begging for help. Sarah comes closer thinking he had an accident and
is shocked to find Nana feeding on a dead Connie. Nana has some weird fungi coming out of her mouth
and when she notices Sarah, she tries to attack her too, so Sarah runs out of the house. At that
moment, Joel and Tommy arrive in the truck. Nana is coming out of the house too, and Joel doesn't
hesitate to kill her, explaining they've seen people losing it like this downtown and the only
solution is to protect themselves. The family leaves in the truck, and Joel tells Sarah that
they say it's some kind of virus or parasite. It's people in the city that got affected,
and their neighbors took Nana to the hospital in the city when she needed her check-ups,
meaning she probably got it there. On their way out of town, they see a house on fire and people
asking for a ride, but Joel tells Tommy to ignore them. When they finally approach the highway,
they find everyone else had the same idea as them and a traffic jam has taken over the road. Tommy
tries to drive through the field, but the army has already arrived and is now blocking the area. They
turn the truck around to cross the town and go North, hopefully they find a clear road to escape
to Mexico. The army planes start flying lower than ever, and the downtown area is a mess: people are
scared and trying to run away, not leaving room for cars to pass through. Tommy tries to go back,
but the truck is now surrounded, and to make matters worse the army is here to drop a bomb.
The truck is hit by the explosion and the family gets knocked out for a few seconds. When Sarah
wakes up, she finds her ankle is hurt, and Joel has to carefully help her out of the truck. At
that moment, a car crashes against the truck and starts a fire, blocking the alley where Tommy had
been standing. The brothers agree to meet outside town and Joel picks up Sarah to go faster, making
his way through the streets that are now filled with infected people feeding on the innocent. An
infected man sees them and begins to chase them, so Joel begins running inside shops and houses to
try to lose him. The infected guy doesn't give up and follows them until they make it back outside,
where he's about to jump on them when suddenly he gets shot by a soldier. Joel asks for help,
explaining they aren't sick, but the soldier receives orders to kill them anyway. When the
man shoots, Joel jumps out of the way, dropping Sarah when a bullet brushes the side of his body.
The soldier is about to try again but at that moment Tommy shows up, killing the soldier first.
Joel rushes to check on Sarah and is devastated to discover the bullet had only brushed him because
Sarah got the worst of it. He tries to stop the bleeding and tell Sarah that is going to be ok,
but Sarah clings to him in fear before dying in her father's arms. Twenty years later, Boston has
become a quarantined wasteland with its borders constantly being watched over by the army. People
do whatever little jobs they're offered by the government, but it's barely a life. One morning,
a young child that was lost outside comes seeking asylum, and the soldiers let the kid in to do the
obligatory checks. A soldier tells the child that everything is going to be ok, but the testing
machine unfortunately indicates infection, so the kid is given a lethal injection. Moments later,
the kid's body is sent on a truck to the pyre where they get rid of infected organisms. Joel
works here sometimes and after so long he isn't disturbed by the fact he has to throw young bodies
into the fire. He often asks for other jobs like street sweeping or whatever will get him paid,
but in secret, he's also working as a smuggler. One afternoon, he attends the public punishment
of a group of people that tried to enter the quarantined zone without authorization. There
he finds a soldier that buys illegal uppers from him, paying with money but also cigarettes. The
soldier also informs him he's finally found a vehicle he can sell to Joel, and they agree to do
the transaction in a few days when the soldiers that can be bribed will be guarding. For now,
the soldier advises him to stay home at night because a resistance movement known as the
Fireflies is causing lots of disturbances, and the guards will shoot on sight without checking
your identity first. The truck the soldier can get his hands on won't have a battery,
so Joel's friend Tess is negotiating with a dealer to acquire one. In fact she already paid to get
one, but the dealer sold the battery to someone else yet spent her money anyway. The dealer's
bodyguards mistakenly beat Tess up when she came to demand answers, and now the dealer doesn't want
to let her go because he's afraid of Joel and what he'll do to his reputation. Their conversation is
suddenly interrupted by an explosion outside that blows up the wall and hits everyone inside. When
Tess finally looks up, the dealer is gone, thus she takes the chance to leave the building through
the hole in the wall, discovering someone had set the bomb on an army truck. Tess tries to get
away as the alarm tells the citizens to clear the area, but as soon as she turns around the corner,
she discovers the Fireflies and the army are shooting at each other in the middle of the
streets. With her hands up, Tess asks the army for help, swearing she isn't a Firefly, but she
gets arrested anyway. Meanwhile in the Firefly's hideout, Ellie hears all the disturbances outside
while being chained to a heater, which has been her situation for weeks now. She told the
Fireflies that her name is Veronica, and whenever a doctor comes to check she's still healthy,
Ellie meets them with sass, tired of having to do the same tests every day without being
given any explanations. In the afternoon, Joel goes to see a friend that has a whole radio set
up and people pay him to send messages to the outside world. Joel offers the cigarettes the
soldier gave him in exchange for news about Tommy, who escaped to Wyoming years ago. They
haven't heard from him in three weeks, which is unusual for him, and today there isn't any news
either. Joel gets tired of waiting and asks for the location of the Wyoming tower, his friend
gives it to him but also points out this is a bad idea because the open country is full of dangers,
like the infected and also slavers. When Joel goes home, he retrieves all the tools he's been hiding
under his floor for his eventual escape and begins preparing a plan on the map to reach the Wyoming
tower. He also gets drunk, and it's revealed then that his watch is broken again, but he continues
to wear it to remember his daughter. Eventually he falls asleep, and when Tess finally comes home,
she just joins him instead of waking him up. The next morning, Joel notices Tess' wounds and she
tells him what happened with the dealer. Joel gets furious because he's desperate for that battery
in order to look for Tommy, so Tess promises him they'll find out who bought the battery and get
it back by force. In the meantime in the Firefly's hideout, leader Marlene is being questioned by her
followers. They want freedom and democracy as much as she does, but they don't understand why they
have to play guards for a random girl chained in a room and why they keep blowing up meaningless army
targets, which is causing them to lose people. Marlene explains the targets weren't random,
they're keeping the army distracted and away from their hideout because tonight,
they're leaving for good in order to take Ellie west to the radio tower in Salem. She shows her
follower the reason why Ellie is so special on a piece of paper, instantly gaining her loyalty
to the cause. Joel and Tess go to the market to pay off some informants that tell them about the
location of the battery, and they agree to enter the building through a hidden tunnel to take the
buyers by surprise. Meanwhile Ellie keeps on trying to break the heater she's chained to,
to no avail. Marlene suddenly shows up and gives Ellie her bag, which includes a knife she loves,
and she finally frees her from the chains as Marlene explains that she was the one that saved
Ellie's life and that she knows Ellie's real name. Marlene was the one that sent baby Ellie
to the military school because she thought she would be safe there, but Ellie complicated things
when she sneaked out. Ellia wants to go home but Marlene won't let her, although she finally tells
Ellie what is the secret purpose that makes her so special, which she mustn't tell anybody to protect
her own life. Moments later, Joel and Tess use the old subway tunnels to move around town unnoticed.
They're quite startled when they find an infected body stuck on the wall so rotten that it looked
like a mutated monster. The pair keeps moving and eventually come to the fake wall they need to move
to access the building, but they immediately worry when they smell gunpowder and see blood
dripping on the floor. When they finally enter the corridor, they find the dealer and his men dead,
it turns out the battery is busted and they were killed for the scam. Suddenly they hear
some noises coming from another room, and when Joel goes to check, he's attacked by Ellie,
who he quickly pushes away. Joel keeps Ellie's knife under his foot and ignores her when she
asks for it, instead concentrating on Marlene and her follower, who are the ones that tried to buy
the battery first. Joel accuses Marlene of being the one that turned Tommy against him, but Marlene
doesn't have time for an argument and explains they need to get Ellie out of the quarantined
zone tonight. Since she and her friend are hurt, they can't do it anymore, and Marlene wants Joel
to do it instead since he's a smuggler. There's a team of Fireflies waiting at the old State House,
and Marlene promises they'll pay Joel with all the supplies he wants if he takes Ellie there
without a scratch. Joel and Tess discuss things and accept the deal, but Ellie doesn't like it
and Marlene has to convince her it's their only option. Ellie gets her knife back and grabs her
bag before leaving with Joel and Tess. They need to wait for the night to fall, so for now they'll
stay at Joel's place. While looking around the apartment, Ellie finds a book about billboard
hits with a note inside that indicates some sort of smuggling code. A song from the 60s meant no
news and something from the 70s equaled new stock, but the 80s only has a red cross next to it. She
asks Joel the meaning behind the cross, but Joel refuses to answer and decides to take a nap until
it's time to leave. Some hours later, Joel wakes up and hears Ellie say she looks forward to being
on the other side of the wall because she's never left the city in her entire life. He wonders if
Ellie is the daughter of some important leader, but Ellie doesn't share her story. Instead she
tells Joel that she heard "Wake me up before you go go" on the radio, which instantly scares Joel.
Ellie smiles and explains it was just a prank to confirm her suspicions about the code: an
80s song equals trouble. At that moment Tess shows up and announces it's time to go. The army patrols
the streets at night to remind the citizens of the curfew, but Tess and Joel have a special
smuggling tunnel that leaves them right outside the border. Ellie can't believe she's outside
and is amazed by a sky with no buildings. The trio sneaks around, hiding behind trash or inside pipes
not to be found by the army lights, but when they turn around an old wall, they bump into a soldier
that is relieving himself. The man immediately makes them fall to their knees, ignoring Tess'
bribe offer, and he uses a testing machine to check if they're infected. Joel and Tess are fine,
but when he approaches Ellie, she stabs his leg with her knife. The soldier points his
weapon at Ellie intending to kill her, and Joel is reminded of the night he lost Sarah. Triggered by
the memory, Joel jumps on the soldier and beats him up until he's dead while Ellie watches. Tess
picks up the soldier's testing machine and is shocked to discover Ellie is infected,
showing it to Joel with fear in her voice. Ellie immediately jumps in to show the marks on her arm
that prove she's had the infection for days but it hasn't spread, meaning she's immune and she
won't turn. They can hear the army coming closer, so they decide to leave this discussion for later
and escape through a hole in the fence, finally leaving the city behind for good.
Meanwhile in Joel's apartment, the radio starts playing the 80s hit "Never let me down again".