The story begins at a lively party where a group of friends are gathered around a table, discussing a mysterious app called Countdown. It supposedly counts down to the moment a user has left to live. Intrigued by the exciting description, the group of friends excitedly download it, and start showing off their life spans as predicted by the app.
Everyone has a handful of decades on the timer, except a girl named Courtney, her timer shows that she only has 3 hours left to live. All her friends laugh it off and treat it as a joke, but she cannot help but be disturbed by this information.
All through the party Courtney remains agitated. Even when it is time to go home, she is reluctant to get in the car with her drunk boyfriend, fearing that an accident may take her life. Her boyfriend thinks she is being ridiculous and drives off in annoyance, leaving her alone to walk home by herself.
The way to her house is not long but in her current state of mind, this short road is very scary. Courtney gets a notification from the countdown app which says that she has broken the user agreement, and she begins getting spooked by every car and every person that she passes by.
Courtney breathes a sigh of relief as soon as she gets through the front door, and securely locks it behind her. But even inside her house, she cannot quite find a sense of security. As the timer on her phone keeps counting down with mere minutes left, she starts feeling even more insecure.
Suddenly, her fears come to life, and she gets pulled to the ceiling by an unknown entity and then just as suddenly, dropped down to the bathroom floor. As the timer on her phone reaches 0, Courtney also loses her life.
The scene then cuts to her boyfriend in the aftermath of his car accident. He sits bloody and injured on his seat, and there is a huge branch impaling the passenger seat. If Courtney was in the car, then she would be impaled along with the seat.
He is quickly taken to a hospital for treatment. However, once he regains consciousness, he cannot get the matter of his girlfriend’s death out of his head.
He is scheduled for surgery, but he is very reluctant to agree, because the same app that predicted his girlfriend’s death shows that he only has a few hours left to live. He has the feeling that he is meant to die on the operating table.
He tells all of these troubles to a young nurse who works at the hospital, Quinn. As expected, she does not believe in the app, and thinks it’s just a silly project made by some loser. However, she is unable to dispel his worries.
This app quickly becomes a hot topic of conversation among her coworkers, as most of them install it on their phones. As they are discussing their lifespans, Quinn also downloads the app, only for it to claim that she only has 2 more days to live.
She dismisses the countdown on the screen, and heads to her childhood home in order to find some documents.
As she is rummaging through the drawers, she finds some noise coming out of the closet. She carefully walks over and pulls open the door, only to see her little sister, Jordan, hiding inside the closet with her boyfriend.
Quinn is disappointed in her, but after their mother’s death, they do not have such a good relationship. She hates the distance between her and Quinn, but due to her older sister’s demanding work, they cannot get enough time to spend together.
As Quinn is attempting to talk to her sister, her father runs into her in the hallway, and reveals his plan for their family to visit her mother’s grave two days later. She easily agrees and then returns to her own house.
The same night, Courtney’s boyfriend is scheduled for his surgery, but because of the app counting to his death, he decides to escape the surgery.
The timer shows that he only has a few minutes left to live. So, in an attempt to escape his fate, he takes advantage of the nurse’s absence and sneaks out of his room.
All of a sudden, he gets a notification from the app saying that he has broken the user agreement. Seeing this, he starts feeling uneasy and ends up running to the stairwell in fear. The lights go out all at once and he is plunged into darkness. The timer on his phone continues ticking down when he suddenly catches a glimpse of his dead girlfriend.
He hesitantly calls out to her, but soon realizes that it is not his girlfriend, but a demon wearing her face. The demon jumps to attack him, and he falls down the staircase and to his death. And the timer on his phone also reaches 0.
When Quinn hears of his death the next morning, she feels her heart tremble in fear. To investigate the matter further, she steals his phone and tries to open it, but finds out that it is locked.
But she is undeterred, even going as far as to pull his dead body out from the morgue, in order to scan his biometrics to unlock the phone.
After she successfully opens his phone, she discovers that his timer really did reach to 0. With her own timer showing that she only has a little more than a day to live, Quinn is understandably disturbed.
She calls her dad to cancel their plan to visit her mother’s grave, but as soon as she does so, she gets a notification on her phone saying that she has broken the user agreement.
The matter of this app is not letting her have any peace of mind. As soon as she gets home, she uninstalls it before looking up information about it on the internet. There is an abundance of news about many freak accidents that were all caused by the app.
But the general consensus among the people on the internet is that the app is fake, and only idiots would believe in such a thing.
Seeing the disbelieving comments, Quinn is a little relieved. However, as soon as she closes her laptop, she sees a gruesome figure of her dead patient standing at the foot of her bed.
But before she even finishes screaming, the figure disappears into thin air, as if it was just a figment of her imagination. She smashes down her phone in fright, and quickly leaves the room but unknown to her, the broken screen lights up again, showing the timer counting down to her death.
Scared out of her mind, Quinn sleeps the entire night inside her car, before she is woken up by Jordan in the morning. Jordan wants to stay with her while their father is out of town, but Quinn is not really in the state to live with her sister at the moment.
Jordan quickly figures out that the reason why she is so frightened is because of the app, that is counting down to her death.
She thinks it is all very ridiculous, and wants to install it herself to prove that Quinn’s worries are unfounded. Quinn instantly jumps to stop her sister from downloading the app.
The two of them get into another argument, before Jordan angrily leaves the house. Quinn wants to reconcile with her sister, but at this moment, she does not have the energy to focus on anything else except for the mysterious app.
That very morning, Quinn goes to buy herself a brand new phone, only to find that the app automatically installed itself on the new phone as well. She is shaken with fear. When she attempts to drive off, a demonic hand suddenly grabs her from the backseat of her car.
She jumps out into the road with a scream, but when she looks into the car again, it is completely empty.
Hearing her scream, a young man named Matt comes to her rescue. He accurately guesses that she is being haunted by the countdown app. He shows her his own timer, and it reveals that he is to die in 18 hours.
With the two of them suffering from the same predicament, they decide to team up and head to a bar together.
While chatting, they realize that the both of them got a notification, saying that they broke the user agreement. Curious as to what the user agreement actually said, they trick a drunkard to install the app on his phone, and carefully read the terms and conditions.
They learn that the user agreement is broken if the user tries to change their own fate. Quinn’s trip with her family, and Matt taking a train ride, which they both canceled, should have resulted in their original deaths.
Confirming that they are dealing with a supernatural entity, the two of them head to the church located in the hospital building where Quinn works. Unfortunately, the priest inside the small church cannot help with anything demonic, but he recommends them to another priest who does.
As they are heading out, Quinn gets tugged away by her coworker. So, Matt decides to head to the toilets while waiting for her.
But he cannot even have this small moment of peace, as the lights suddenly go out and he is haunted by a monster pretending to be a little boy.
The monster jumps to attack Matt, but he manages to protect himself until another person enters the room, and the surroundings instantly return to normal.
Frightened, Matt quickly joins up with Quinn again, before heading to another church to find the priest specializing in demons.
The priest is not nearly like they imagined him to be. He seems to have an obsession with demons, as he rambles about them like a nerd. Listening to their description and experiences, he declares that the demon haunting them is called Ozhin.
It is the demon who tortures people who try to escape their fated death, until the moment they die.
Unable to do nothing about their impending deaths, Matt and Quinn decide to try a hand at hacking the app. They drive to the phone clerk, who sold Quinn her new phone that morning, and try to get him to hack into the app.
The clerk is reluctant at the beginning, but after some bribing he swiftly opens the shop again, and begins working on his computer.
To his surprise, he finds that the app is worth 60GB, which is a lot for a simple timer app. What’s even weirder is that the code is written in Latin.
After some fiddling around, he manages to find a huge database of users and their timers, that are slowly ticking down. While scrolling around, Quinn notices that her sister’s name is on it too, and her timer ends just a few minutes before Quinn’s.
Knowing that her sister secretly downloaded the app as well, she asks the clerk to add a few decades of time for all three of them, herself, Matt and Jordan.
To their pleasant surprise, this plan actually works, and they can see the timer increasing the years of their life right before their eyes. Even though they are now in the clear, Matt and Quinn do not want to spend the night alone, so they decide to be together at her house.
Later, while they are sleeping, the lights suddenly go out and Quinn spots a shadow lurking outside her bedroom door. Panicking, she shakes Matt’s arm to wake him up, but before he could, the door swings open revealing Matt, who is confused by her words.
Quinn screams in terror, the arm that she was touching was in fact the demon who tricked her. The demon is gone as quickly as it came, but right at that moment, they see their phone’s timer resetting to their original lifespans.
At the same time, Jordan is in her own house, sneaking around in the dark. She is trying to get her phone back from the babysitter, who seized it earlier that night, but as she gets back into her room with her phone, she notices weird occurrences with the lights.
Frightened, she quickly hides under her bed, but suddenly, she begins hearing the voice of her dead mother. The voice grows increasingly menacing by the moment, until Jordan cannot take it anymore and runs out of the house in terror.
Thankfully, she runs into Quinn and Matt who came to pick her up. The three of them immediately drive to the church where they meet up with the priest again. He reveals an idea that is sure to work, they have to prove that the devil is a liar.
It means that they just have to beat the timer by even a second and stall for time so that the timer is proven wrong.
He comes up with a plan to draw a ritual circle on the floor, that is able to keep demons away. And for a moment, the circle works. No matter how frightening the demon is, as long as they stay inside the circle, it is not able to harm them.
However, the demon is full of tricks. Seeing that it cannot enter, it decides to lure the people out. It takes the form of Matt’s younger brother, and as if put in some sort of spell, Matt willingly follows the demon. As soon as he steps out of the circle, Matt’s body is dragged away in an instant.
Quinn follows right after him to save him, but she sees that he is outside in the front yard, completely uninjured. But before Matt has the time to rejoice, a car speeds in out of nowhere and crashes against him. As the timer in his phone reaches 0, Quinn witnesses Matt lose his life right before her eyes.
Quinn feels defeated but she has no time to waste, as Jordan starts bleeding from her stomach. She immediately takes her sister to the hospital, where she receives swift treatment from Quinn’s senior doctor.
The doctor has a history of misconduct against his female coworkers, and coincidentally, he also has a few decades of time left of his lifespan.
Quinn immediately gets an idea. There are less than 20 minutes left for her and Jordan to live, so she is willing to go to any lengths to survive.
She cleverly lures the doctor to follow her to the abandoned section of the hospital. While he excitedly searches for her through the abandoned rooms, Quinn quietly lies in wait with a metal pipe.
As soon as the doctor comes in her range, she slams the pipe against his body and begins attacking him in earnest. She wants to kill him despite his long lifespan, and prove the demon is a liar.
It is now the only way for her and her sister to survive. But as Quinn had expected, the demon will not let the doctor die before his fated end. So, before Quinn has the chance to end his life, the demon intervenes and drags the doctor away.
Jordan finds Quinn in this murderous state and tries to discourage her sister, but Quinn is nothing but determined to trade in the doctor’s life for theirs.
She searches through the abandoned floor in hunt for the doctor, but he finds her before she has the chance to find him. He sneaks up to attack her, and is determined to take her life in revenge. But Quinn is not the one to go down so easily.
She fights back with all her might, and manages to turn the situation around in her favor. But unfortunately, there is a demon helping the doctor. And so, despite Quinn’s struggles, he manages to escape from the building without any injuries.
At the same time, in the same building, Jordan’s time is quickly coming to an end. As the timer reaches closer and closer to 0, the demon starts coming after her. Trying to escape is no use, as it is able to find her no matter where she hides.
When she has less than a minute on the timer, the demon reveals itself and begins attacking her. Jordan screams for help and to her surprise, Quinn arrives just in time with a syringe in her hand. Since she could not kill the doctor ahead of time, then she can just kill herself.
Seeing as she is ready to give up her life, the demon takes the shape of her mother and tries to trick Quinn into letting go of the syringe. But these cheap tricks have no effect on her, as she fearlessly injects the liquid into her arm despite Jordan’s pleas not to.
Her breathing instantly stops, and the demon rushes in to save her, but it is already too late. Quinn has managed to prove that the demon is a liar, and it scatters away into the air.
The demon is defeated but Jordan is grieving the loss of her sister. As she cries and cradles Quinn’s body, she notices that there is a name of a drug written on her arm.
Right at that moment, a vial of drug rolls on the floor, and Jordan instantly realizes what she must do. She quickly uncaps the vial and injects the liquid into Quinn’s arm, with the help of a syringe inside her pocket.
Only a moment later, Quinn takes a deep breath, coming back to life from the jaws of death. And the two of them tightly embrace each other, having successfully survived a terrifying ordeal.
A few days later, when the dust has settled down, Quinn and Jordan make a trip to visit the grave of their mother.
The relationship between the two sisters has only gotten better these days, and they are now closer than ever.
Just as they are leaving the cemetery, Quinn’s face instantly darkens as she sees a notification, an app called countdown 2.0 installed itself on her phone.
Shortly after, the phone clerk who helped Quinn hack the app, is on a date with a woman.
Suddenly, the lights go out and the screen goes blank, as demonic screams echo in the background.