After losing the boat during an accident, an unconscious Jenn washes ashore on an island. When she wakes up, she sees her friend Brad nearby and runs to check on him, only to discover he’s got a large piece of coral sticking out of his stomach. She yells for help but nobody answers, so after taking the flare gun from his vest, she drags Brad away from the shore.
She removes the coral to then cover the wound with some fabric yet Brad’s only response is asking “did you see it? ”. Jenn thinks he needs some water so she runs into the jungle to find a coconut and breaks it with a rock.
Unfortunately by the time she returns, Brad is already dead. Afterward Jenn explores the island but walking down the beach just makes her do a full circle until she’s back where she started. Then she explores the jungle and finds a bunch of stuff that’s been there for a while judging by its condition.
Jenn yells for help again but nobody answers, so she searches the bag and finds some medicine. Next she checks the cooler and finds some sealed soda bottles. There are more objects under some leaves like a little metal box in which Jenn finds matches, some sailcloth, and a bag with toys.
Suddenly Jenn hears a weird noise and goes looking for the source. It’s coming from a hollow tree and when she looks inside, she’s startled by a bird flying out. Then Jenn covers Brad’s body with some big leaves.
Noticing the sun setting, she looks for a spot to spend the night right before it starts raining. She covers herself with the sailcloth and leaves some things out to collect water. The following morning Jenn finds tons of dead fish on the shore and begins collecting them in a bag.
She’s also shocked to find a dead shark with nasty gashes on its body. Jenn uses rocks to cut all the heads off and keeps the fish in the cooler for later consumption. While looking through another bag, she finds a notebook and tries to read it, but the water has erased all the text.
Among the pages there’s a picture of a couple that makes her feel extra lonely. The next time Jenn explores the island, she finds some piles of rocks and a cross-shaped branch, which makes her realize those are graves. This inspires her to dig a hole in the sand and throw Brad’s rotting body in it to then cover it with leaves and sand, finishing the grave with a piece of wood with Brad’s initial.
That night Jenn hangs the sailcloth, which has gashes that match the shark, and starts a fire with the matches to cook the fish. In the morning, Jenn is horrified to discover Brad’s body is missing and the grave is full of blood. Realizing there’s something dangerous out there, she uses a rock on a branch to make a spear.
She also brings a log to use as support so she can spend the evening sitting with her eyes on the jungle. Eventually Jenn falls asleep and is woken up in the middle of the night by a strange noise. However she can’t see anything among the trees and assumes it was the fire.
The next day Jenn notices some items floating nearby and gets in the water to retrieve them. Before swimming back, she dives to check if there’s anything else and she’s shocked to see a mysterious hole in the ocean’s floor. She doesn’t dare to go closer and returns to the shore with her new things.
Inside a suitcase she finds a bunch of clothes and changes into something warmer. That night Jenn checks the box again and discovers pictures of the dead owners. Suddenly she hears a plane fly by so she immediately runs to the shore to shoot a flare, but unfortunately the plane doesn’t see it.
As the flare falls into the sea, it reveals the silhouette of a strange tall monster. A terrified Jenn hurries back to grab her spear and runs to hide in the jungle. Soon the monster steps on the island and searches among the bushes, but it doesn’t see Jenn and leaves without attacking.
The following morning Jenn notices the monster made a mess out of her camp. When she picks up the old pictures, she discovers the monster’s eyes in the background. Desperate to escape, Jenn puts Brad’s and her life vests inside the suitcase, then she takes it to the water.
She intends to use it as a raft but the suitcase isn’t stable enough to support her weight and Jenn throws it back on the sand with lots of frustration. Before the sun sets, Jenn hides inside the hollow tree to sleep safely. Later in the middle of the night, she’s woken up by the noises of the monster arriving to the island.
It grabs her log to begin rolling it and pounding on it, so Jenn has to concentrate not to make any noise and protect her head. After lots of shaking and growling, the monster gets bored and finally leaves. Days pass with Jenn surviving during the day by fishing and during the night by hiding in a hole.
After some practicing, she finally manages to kill a small shark with her spear. She hangs it on a tree before falling asleep in the hole, but she still hears the noise of the monster taking the shark away. Sometime later, the waves drop another body on the shore.
When Jenn checks on it, she discovers severe face wounds caused by the monster, not to mention it’s missing the legs. She hangs it on the tree and hides in her hole, but this time she stays awake to watch the monster arrive. It quickly brings the body down and starts feeding on it.
At that moment Jenn hears a plane fly by and gasps, but she can’t come out because the monster is walking near her hole. When it fails to find her it goes back to the ocean, but unfortunately the plane is already gone. The next day Jenn uses the sailcloth, some belts, and rope to make a hammock that she hangs high on the trees.
Now she can have a better view of the area from above and stay out of the monster’s reach. That night, Jenn is comfortable in the hammock when she notices the monster walking among the bushes. Suddenly it starts pulling at the ropes to bring down the hammock, causing Jenn to scream and struggle in the sailcloth until she falls off.
She immediately starts running away as the monster chases her, jumping in and out of the water to move faster by swimming. Eventually it lands in front of her and a terrified Jenn stabs it with her spear, only for the beast to throw her on the sand. Then it hits her again and she lands in the water, but before the beast can kill her, a sudden thunderclap scares it away.
Jenn decides to climb on a tree and sleep there under the rain, even if it’s a very uncomfortable position. In the morning, Jenn checks her leg and finds a nasty wound. While she washes and changes clothes, she sees a life raft floating nearby and immediately jumps in the water to reach it.
There are two people inside: her boyfriend Lucas and Brad’s girlfriend Mia. Jenn helps them reach the shore and the couple reunites with a tight hug. Then Jenn shares her fish and the sodas while trying to tell her friends about the monster, insisting they should use the raft to leave.
She even shows them the picture and tells them about Brad’s death, however Lucas and Mia don’t believe her. They think she’s been seeing things and they refuse to get back on the raft because the isolation almost drove them mad. Afterward Jenn announces she’ll get more food and borrows Lucas’ Swiss knife.
When she opens it to clean the fish, she notices blood on the blade and gets suspicious. She tries to convince her friends to leave again and an argument ensues that ends with Lucas yelling at her. Later while Lucas and Mia are distracted, Jenn gathers her things and puts them in the raft before pushing it to the ocean to escape.
However her friends see her and run to stop her. Lucas grabs Jenn and in the struggle, she kicks Mia in the face. Furious, Mia retaliates by knocking Jenn out with an oar.
It’s nighttime by the time she wakes up and she’s horrified to discover her friends have tied her to a tree. They refuse to untie her when she asks, and Mia leaves to give the couple some privacy. Lucas begins complaining about Jenn’s attitude, mentioning how he had been having fun in the boat with his friends yet she wasn’t happy and even threatened to break up with him.
Jenn thinks this isn’t the right moment to discuss their relationship but Lucas keeps going, yelling about how Jenn has no home, no money, and no life without him. He thinks she had no right to try to abandon him on the island after everything he did for her. As Jenn insists on leaving and talking later, Lucas points out she’s sounding too much like his friend Zack, but he doesn’t say what happened to him.
Meanwhile Mia is walking on the shore and notices some fish pieces in the water. Suddenly Lucas and Jenn hear Mia scream, so Lucas grabs a torch and runs to help her. He finds the monster killing Mia and hits it with the torch, only for the beast to push him away.
Then it jumps into the sea and takes Mia with it. By the time Jenn finally cuts the ropes off, it’s too late: there’s only blood left in the water. The next morning Lucas finally agrees to leave in the raft with Jenn.
They work together to get a bunch of fish and cook them all with a fire made from the last match, this way they can bring provisions to the trip. Afterward they put all their things in the raft and take off at last. Inside the raft, Jenn is surprised to see multiple bloodstains.
As Lucas starts to row, he suddenly sees the creature swimming under them. Its claws reach out to attack Lucas, who immediately hides inside the raft and Jenn closes it up. However the monster doesn’t give up and starts scratching the bottom of the raft.
After a few hits that make the whole structure shake, the monster punches a hole and pokes its head in. Jenn immediately kicks it and Lucas starts shooting the flare gun. The first time he misses, but the second flare lands in the beast’s mouth.
The duo then uses the chance to push it back into the water with the spear. For a second they think they’re safe, however the creature reaches through the raft base again and drags Jenn underwater, intending to take her to his hole. While she struggles against its hold, Jenn remembers Lucas’ dagger and uses it to stab the beast, who lets go of her and swims away.
At that moment it sees Lucas jumping in the water to rescue Jenn and quickly swims towards him, grabbing him at the last second to then drag him into the hole. After yelling in grief, Jenn swims back to the shore and notices the fire they supposedly put off still has a little spark left. Jenn runs to work on rekindling it until proper flames appear again.
Afterward she grabs the notebook and writes a letter explaining what’s happening in case she dies and someone finds her. Jenn has a plan in mind which includes making a bunch of spears, gathering wood and leaves, and digging holes in the sand. This causes her to find a skeleton, so she decides to use the bones for her plan as well.
When night falls the monster comes out of the water and starts wandering through the jungle, following the smell of fish. Once the beast reaches the bait, Jenn lights a bunch of pyres on fire to trap the monster in the middle. Then she surprises the creature with her spear, stabbing it once before running to hide behind a tree.
The monster goes looking for her and Jenn waits to have its back on her so she can stab it with a bone, only to quickly be knocked down. She doesn’t give up and immediately stabs the monster again, so this time it hits her hard enough to send her flying. Noticing that the beast is bleeding and in pain, Jenn decides to keep on fighting.
She stabs it over and over again with any piece of bone she can find, sometimes getting hit in the process. The creature pushes Jenn down on the sand and she stabs its arm to free herself. Then it grabs her legs and pulls her closer to pick her up by her face, ready to finish her.
Jenn takes out one last piece of bone and repeatedly stabs the wound she left earlier to force the monster to drop her. It hits her with its claws one more time, however the pain is too much and it can barely move anymore. Jenn uses the chance to run back to the beach and grab more spears.
Soon the monster catches up to her, but after roaring very loudly it collapses on the sand. Since it’s still breathing Jenn stabs it with the spear until it’s finally dead for good. Then she takes a piece of its very hard shell and uses it to cut the monster’s head off.
With the head as proof of what happened, Jenn begins making her way to the raft while the jungle burns behind her.
