In the near future, scientists manage to reprogram the measles virus to help cure diseases instead
of causing them, and they even manage to cure cancer. However they lose control of this virus
and it ends up infecting most of the population, transforming them into dangerous mutants called
Darkseekers, who feed on people and are weak to sunlight. Three years after the initial outbreak,
New York City is a complete wasteland, to the point where the zoo animals now freely walk around
the streets. The only survivor is Robert, a former army virologist that spends his days with his dog
Sam. Whenever they go hunting, Sam helps Robert find the animals, and he chases them through the
streets in whatever car he fells like taking that day. Robert is always armed and a great shooter,
but he also has a good heart and when he sees families of lions hunting too, he lets them
have the meat. He also keeps an alarm on his watch to make sure he isn't out when the sun
sets. As soon as the alarm goes off, Robert rushes back to the same house he's lived in since before
the outbreak, which has been fortified to the max. Robert can shut all the doors and windows,
and he always makes sure to bleach the front steps so that the Darkseekers can't find his smell.
Inside this house, Robert keeps a good supply of food and tapes of old newscasts that allow him to
stay sane by pretending he's going through an old routine. He also listens to music, talks to Sam,
and does the usual chores like bathing his dog and cooking for both of them. No matter how much
he tries to distract himself though, his dark memories always crawl back: when night falls,
he hides in the tub with Sam and some firearms, and the sound of the Darkseekers outside makes him
think of his family. When the outbreak happened, the government decided to seal off the island,
since it was ground zero. Panic took over the streets as people tried to escape in hoards.
Robert rushed to pick up his wife Zoe, their daughter Marley, and Sam, who was still a puppy
back then. He wanted them to leave the island to stay with a relative, and Zoe got angry when she
realized Robert wasn't coming with them because he wanted to stay to analyze the virus and find
a cure. This triggered an argument between them that almost made Robert crash the car. Robert
hasn't given up on the idea of a cure even in the present. Every morning after exercising with Sam,
he goes to the lab in his basement to keep track of his experiments. Sam isn't allowed down there
because she could get infected, but Robert is fine because he's immune. In the lab, there's a
bunch of caged rats carrying the virus, and Robert has been trying the different serums he's made on
them. All of them failed until one morning, Robert discovers one of the rats is actually getting
better. Now he can move on to the next step of the trial, but he'll need a human for that. Afterward,
Robert and Sam visit the video store, where Robert has put up a bunch of mannequins as part of trying
to keep the illusion of a normal routine. He talks to them as if they were old friends and
always brings back the movies he takes before choosing another one, he also pretends one of
the mannequins is trying to flirt with him. Robert promises Sam that one day he'll flirt back. Next,
the pair visits the parks where Robert is growing vegetables to take some with them. They also keep
a map of all the houses they've already visited and choose a new one to do each day. This allows
them to find new supplies of food, although the things they find the most of are medicine and
cleaning products left behind by the fight against the outbreak. Sometimes Robert also
finds really depressing signs of the people that used to live there, like the bodies themselves,
or even nurseries that never got to be used. After picking up gas for the car, Robert proceeds with
the last part of his routine, which consists of going to the South Street Seaport to broadcast a
recording that invites any survivors to meet him there. While he waits he keeps himself entertained
in different ways, like playing golf on top of the air force's planes. One afternoon, Sam notices a
deer running around, so she and Robert begin chasing it through the streets. The deer panics
when it comes across a blocked road and enters an old, dark building. Sam follows it inside,
which makes Robert nervous because such a dark place could be the perfect nest for Darkseekers.
Since Sam won't come out when she's called, Robert has to enter as well, and he tries to be as quiet
as possible not to give away his presence. There are some terrifying noises that suddenly scare
Robert, but he refuses to leave without Sam, so he takes a moment to gather courage and cover
his flashlight with his hand before going deeper inside. He follows a trail of blood upstairs that
takes him to a body behind some furniture, for a moment Robert fears the worst until he realizes
it's not Sam, it's the deer. As he continues his search, Robert finds a bunch of Darkseekers
standing near a wall, thankfully he reacts fast and steps back, keeping his flashlight away from
them. Robert turns around and finally finds Sam hiding under a desk, refusing to come out because
there's something that scares her. At that moment, a Darkseeker jumps on Robert from behind. Robert
immediately shoots him before running away with Sam, telling the dog to take a different corridor
when the other Darkseekers begin chasing him. With a plan in mind, Robert runs to the window
and jumps right when the Darkseekers catch up to him, this causes the sunlight to kill the
two monsters that fall with him on the ground and keeps the others inside. After reuniting with Sam,
Robert prepares a special trap using a truck on a bridge and some old canvas that the puts down
at the building's entrance. He tells Sam not to follow him for this one to avoid infection, then
he takes some of his own blood and drops it on top of the canvas. As soon as a Darkseeker comes
closer to feed on the blood, the trap activates, making the truck fall and drag the Darkseekers out
inside the canvas. A second Darkseeker, considered the Alpha of the group, peeks out of the building
to roar at Robert with clear fury, only to quickly go back when the sunlight begins burning him.
Moments later, Robert has the female Darkseeker he caught in his lab, strapping her to the table
in order to test the cure he's been developing. He first uses UV light to confirm she's infected with
the virus, and he discovers she's got a butterfly tattoo. Robert begins by injecting the serum he's
created from the rat that did well, and after a few seconds of nothing, the Darkseeker suddenly
begins screaming and struggling against her shackles. After a moment of panic, the Darkseeker
passes out, and all her vital signs go to zero on the monitor. Robert immediately gives her
a new injection to keep her alive, but he also can't help shaking the furniture with anger at
the failure. Then he puts the Darkseeker behind a glass door before logging his progress for the
day, mentioning the fact Alpha Male exposed himself to sunlight on purpose. This makes
him think that decreased brain function or the scarcity of food is causing them to ignore their
basic survival instincts, and social devolution appears complete. That reminds Robert of the day
of the outbreak again because people were behaving like crazy on the streets. Lots of ships were
leaving the island, but only those with clearance were allowed to pass, and people didn't like being
left behind in quarantine, especially those with kids that begged others for help. The roads had
been blocked by the army, but the soldiers had orders to escort Robert and his family to safety,
thus they continued on foot. When they reach the harbor, the soldiers used a scanner to make sure
they weren't infected, Marley passed but Zoe didn't. Mother and daughter panicked because
they didn't want to be separated, prompting Robert to make a scene and pull rank to order a second
scan. Zoe passed the test this time, and because they were an army family, they got to leave on a
helicopter. Robert insisted on staying and said goodbye to Zoe and Marley, who decided to leave
Sam with him so she could protect him. As the helicopter took off, Marley made a butterfly
with her hands as a goodbye. Back to the present, Robert and Sam go through their usual routine,
but at the end of the day when they're about to go home, some strange happens. There's a mannequin
near the bridge, and Robert is sure he didn't put it there. Feeling like he's going crazy, Robert
shoots at the mannequin as if to prove it isn't real, the mannequin just falls to the ground. Then
Robert thinks he can hear some whispering around him and begins shooting at the air like crazy.
Since nothing happens, Robert decides to check out the mannequin, but as soon as he comes closer,
a car falls and he's caught by a rope: it turns out the Darkseekers copied his trap. Sam hits his
head and he passes out as blood begins to drip on the ground. Moments later, Robert wakes up
when his watch's alarm goes off. Sam is still there, and the sun is about to set, so Robert
uses a knife to cut off the rope. When he falls to the ground, he hurts his leg, and now he has
to drag his body through the ground to leave. Sam at first follows him, but she stops when she hears
some growling coming from a building. The Alpha is there with a bunch of infected dogs and he
sets them loose to go after Robert, but the dogs step back when they almost get hurt by the last
bit of sunlight. Robert forces himself to stand up and rush to his car to retrieve a gun right before
the sun finishes setting, allowing the dogs to attack. One of them jumps on Sam and bites her
while Robert fights the others, struggling against a beast before managing to grab his gun properly
and shoot them all one by one. Sam is in pain, so Robert ignores his own to pick her up and take
her to the lab, where he gives her a dose of his serum. Then he holds her in his arms and sings a
song for her, but little by little, Sam's starting to turn. Devastated, Robert has no choice but to
euthanize her, ignoring her barks of protest until she's dead. After grieving her properly,
Robert gives Sam a burial in the garden before trying to go back to his routine. He takes a lot
of medicine to try to forget the pain, and when he goes to the video store, he finally chats with the
flirting mannequin, saying he promised his best friend he would do so. Obviously the mannequin
doesn't talk back, and this causes something in Robert to finally break. Furious and miserable,
Robert takes his car out at night to run over a bunch of Darkseekers in revenge. He manages to
kill a few of them but the others attack him under the Alpha's orders, they even climb a light post
to make it fall on top of Robert's car. Then they flip the car over to get Robert stuck inside, but
when the Alpha enters the car through the window, an UV light suddenly blinds them all and causes
the Darkseekers to flee. Robert isn't feeling well because he hit his head when the car was flipped,
but he can tell there's another person taking him away in their car. This person asks where to take
him, so Robert gives them his address and asks them to make sure they aren't followed before he
passes out. That night, Robert dreams of his family again. After the helicopter took off,
the government bombed the bridge to seal off the island. One of the helicopters lost control when
people tried to jump on it, and it crashed against the one with Robert's family, instantly killing
them. The next morning Robert wakes up to the sound of an animated movie on his tv. The wound
on his leg has been stitched, but he's still wary and he grabs a gun before going to the kitchen,
where for a moment he thinks he sees family again. In reality this is Anna and her son Ethan, they
were the ones to save him last night. Anna has made breakfast, so Robert puts down the gun and
sits with them, hearing Anna's story. They come from Maryland, and they stopped by the harbor when
they heard Robert's message. They're making their way to Vermont because there's a safe zone full of
survivors in the mountains, where the cold should keep the virus away. Robert refuses to believe it
and tells Anna that everyone's dead as he tosses his plate to the ground with anger. Realizing how
close he is to losing it, Robert goes upstairs to have a minute alone. Once he's calmed down,
he joins the others again and takes the chance to quote the movie to prove to Ethan that he
means no harm. Robert confesses he loves that film, and it's quite obvious he identifies with
the ogre because he also has no friends. Once Robert thanks Anna for the rescue, they have a
little chat. Anna explains she had been on a Red Cross evacuation ship out of San Paolo,
but those boats weren't made to be permanent. When the Navy fell apart, Anna's group returned to the
shore to search for supplies, and someone stole their boat. Five people in her team were immune,
but they were killed by the Darkseekers. She still intends to go to Vermont, but Robert refuses to go
with her, explaining he wants to stay at ground zero and work on a cure. Later, they go to check
the area where they found Robert last night and he checks the trap, noticing it was made
from the tools they took from his own trap. Robert doesn't want to believe the Darkseekers did this
because they aren't supposed to have higher brain function, meaning they shouldn't be able to plan,
hate, or love. Anna thinks the Darkseekers could possibly be evolving. Afterward they take Ethan to
have some fun in a fountain, and when Robert hears Ethan complain about the cold water, he gets an
idea. The trio returns to the house, where Robert puts the female Darkseeker on top of lots of ice,
thinking that changing her body temperature may help the serum work better. Anna looks around the
lab and discovers a bunch of pictures that show Robert has tested many versions of the serum on
humans before, but they never worked. Afterward Anna finds Ethan fell asleep on the couch,
so Robert offers to take him to his daughter's old bed. Anna finds the pictures of Robert's family
and he tells her a bit about them, explaining his daughter was named after Bob Marley, who Anna
never heard of before. Robert can't believe this and immediately plays his favorite CD for her,
confessing Bob Marley was his inspiration because he kept on singing even after he was shot at his
own home. When night falls, Robert seals all the windows, and again Anna tries to convince him to
come with them. Robert wonders how she can be so sure there's a colony, and when Anna says
God told her, Robert finally snaps. He yells at her as he points out that most of humanity
is dead and the rest became monsters, meaning there's no God. Their conversation is suddenly
interrupted when they hear some noises outside: it turns out the Darkseekers followed the smell
of the blood he dripped last night and they're now here. Anna rushes to get Ethan while Robert turns
on the lights that he installed outside, but the Darkseekers just jump on them and destroy them.
Next Robert activates a bunch of explosives he buried just in case, killing the first
hoard. Afterward Robert goes upstairs to look for Anna, only to suddenly be jumped on by the Alpha.
The two of them begin to fight and Robert uses a screwdriver he finds on the floor to attack him,
but the Alpha barely feels any pain and throws Robert back downstairs. Robert uses the chance
to steal a weapon he hid among the umbrellas, and when the Alpha dodges the shots to hide
in another room, Robert shoots a gas canister to cause an explosion. The Alpha runs upstairs again,
and Robert follows him with open fire until he sees the Alpha jump out of the window. Afterward
he goes looking for Anna and Ethan, finding them hidden under some furniture while a Darkseeker
destroys the ceiling of that room. There's a gun on a table nearby, so Robert rushes in,
grabs the gun, and shoots at the monster right as he turns to attack him. At that moment,
Robert hears a noise outside and discovers the Alpha is back with even more Darkseekers,
thus the trio runs to hide in the lab. As the Darkseekers climb the building to enter through
the hole their friend made, Robert and Anna are shocked to discover the female test subject is
getting better. This means the cure is working, but before they can consider their options,
the Darkseekers arrive at the lab and Robert has to close the glass door between them. He tries to
tell them he can save them, but the Darkseekers don't listen, they just keep on hitting the door.
When the Alpha arrives too, he cracks the glass with his mighty strength, then he makes a drawing
that Robert recognizes as a butterfly, just like the woman's tattoo. This reminds him of Marley,
and Robert finally understands the Darkseekers do have feelings - they're here to rescue their
friend, not to kill. Robert puts down his weapon and, ignoring Anna's protests, disconnects the
woman from the machines before taking her out of the glass door. As the Darkseekers
growl at him with fury, Robert picks a syringe and injects the woman with some medicine that
causes her to wake up. The Alpha immediately rubs his forehead with hers, celebrating their reunion
before picking her up to leave. Robert tries to apologize, but he's only met with another growl.
Now that Robert understands the city belongs to the Darkseekers' society, he accepts to leave
with Anna and Ethan. The next morning they start their trip to Vermont, but first Anna
makes a new recording, telling any survivors that may listen where to find the safe colony.