NOTE: This spoiler was submitted by Jeremy

The film starts in the woods. A boy in a yellow jacket appears injured as he runs for his life. He stops in the middle of the woods, falling on his knees and breaking down in despair.

Somewhere in Britain, five teens – Nolan (Jack Kane), Bess (Sophie Jane Oliver), Queenie (Molly Dew), Reggie (Zak Sutcliffe), and Karl (Zander Emlano) – are going on a field trip with their bus driver Joseph (Terence Anderson). Karl teases Queenie, while it appears that Nolan likes Bess, and Reggie just sits in the back waiting to cause trouble. Joseph gives the teens a riddle to solve to pass the time, involving seven letters and being a much-needed virtue. On the road, a fallen tree blocks their path, so Joseph decides to take an alternate route.

Further up, Joseph exits the bus to move a dead animal from the street. When he returns, he is held at gunpoint by escaped convict Pedro Minghella (David Keyes), whom Karl recognizes from the news. Pedro hijacks the bus and orders everyone to let him ride with them, and they have no choice but to comply. He also forces them to throw their phones out so that there’s no way that they can call for help.

Joseph drives the bus later into the evening until they enter a tunnel where the bus stops running. Pedro forces Joseph to fix it by holding Queenie hostage. The lights in the tunnel suddenly go out, leaving everything in pitch black darkness, save for the bus headlights. With his flashlight, Joseph walks up to see something sitting in the middle of the way. Once he gets close enough, the thing reveals itself to be a monstrous creature that rises and kills Joseph, to the horror of the teens. To make matters worse, he had the keys on him. After an argument, Bess volunteers to go out and retreive the keys. She succeeds and makes it back to the bus safely, and Pedro forces Reggie to start the bus with a gun to his head. Reggie tries but eventually manages to take the gun from Pedro…only for a momentary distraction to let it back into his hands. He goes outside to try and kill the beast, only for it to sneak up on him and rip his head off. The monster (which looks like a weird alien with sharp teeth and long hair) tears out the wiring on the bus and hop on board, but the teens manage to escape.

The kids get far enough but still don’t have an exit. They realize the creature is sensitive to light, so they must find a way to turn the lights back on in the tunnel. Nolan and Bess go off to find the main generator while the other three stay together. Nolan comes across some evidence that someone else knew about the creature and had tried to kill it. He and Bess find pictures and journals, as well as countless drawings of someone obsessed with killing it. Meanwhile, Queenie asks Reggie to escort her to pee, but when he has his back turned, the creature grabs Queenie. Reggie gets Karl to help, and they find the creature biting into Queenie. They fight it off with torches and rescue her before the wound becomes fatal. The creature then gets Reggie and nearly kills him until Nolan and Bess manage to turn the lights on, scaring the creature away.

After Nolan and Bess catch up with Reggie, Karl, and Queenie, they show the three all the evidence they found. It belonged to a man named Giulio Sarpi, who, in 1971, lost his younger sister Isabella to the monster (he was the boy seen in the film’s opening). Giulio spent 40 years studying the creature and learning how to try and kill it, only to end up killed by it instead. His corpse is found by the teens in a corner. They decide it is time they kill it themselves.

The kids devise a plan and find a way to lure the creature toward them. Bess and Queenie get the creature to chase them until they find the exit to outside, where it is now daytime. The creature stops and is trapped when the boys come running up to it with torches. With nowhere to run, the creature can only stand as they light it on fire. It writhes and screeches until it finally collapses, apparently dead.

The teens walk together into town to get help. Sometime later, they are seen hanging out, closer than ever. Their voiceover narration reveals that they solved the answer to Joseph’s riddle – it was courage, which is what it took for them to work together and be free.

Authorities later come by the tunnel to investigate the teens’ story. One detective goes in with a flashlight, only for the light to suddenly go out. He hears the croaking/rattling noise from the creature, who then appears behind the detective.

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Five teens - Nolan, Bess, Queen, Reggie, and Karl - are on a field trip with their bus driver Joseph, when they must take a shortcut after a fallen tree blocks their path. They are hijacked by escaped convict Pedro, who forces them to drive him. Driving into the night, the bus breaks down in a tunnel where the lights all go out. Joseph investigates and is killed by an alien-looking monster. Although they try to escape, the monster kills Pedro and forces the teens to run from the bus into the tunnel.

The teens try to find an exit by finding the light generator. Queenie and Reggie are almost killed by the monster, but Nolan and Bess manage to get the lights on and scare it away. They also find evidence of a man named Giulio Sarpi, who lost his younger sister to the monster as children, and he spent 40 years of his life trying to find a way to kill it, only to be killed himself.

The teens come up with a plan to escape and kill the monster for good. Bess and Queenie run to the tunnel's exit where it is now daytime. The boys trap the monster between them and torch it to death. The kids go to town and are safe, but as detectives investigate the tunnel, the monster appears to be alive and attacks a detective.