In the opening scene of the movie, a boy dressed in a yellow jacket appears injured, desperately running for his life through a dense forest. He eventually collapses on his knees, overcome with despair and exhaustion, as the scene shifts to a group of five teenagers in Britain setting out on a school field trip. The group consists of Nolan, Sophie Jane Oliver as Bess, Queenie, Reggie, and Karl. Their bus driver, Joseph, played by Terence Anderson, is guiding them on their journey when he presents them with a riddle about seven letters and a vital virtue, adding an element of mystery and challenge to their trip.
As the bus travels through the countryside, it encounters a fallen tree blocking their path, prompting Joseph to take a detour. During this detour, Joseph steps out of the bus to remove a dead animal from the road. When he returns, he is unexpectedly threatened at gunpoint by Pedro Minghella, a escaped convict recognized from the news by Karl. Pedro, portrayed by David Keyes, hijacks the vehicle and forces the teenagers to comply with his demands: he makes them throw their phones out of the bus, ensuring they have no means of calling for help. The situation escalates as Pedro holds Joseph hostage, demanding that he repair the bus while threatening Queenie.
The tension reaches a breaking point when the bus enters a dark tunnel. The vehicle abruptly stalls, and Pedro compels Joseph to fix it under the threat of harm. Suddenly, the tunnel's lights black out completely, leaving the bus shrouded in darkness except for the headlights. Armed with a flashlight, Joseph investigates and encounters a terrifying creature sitting motionless in front of the bus. As he approaches, the creature reveals itself as a monstrous being with sharp teeth and long hair—an alien-like entity that swiftly kills Joseph, leaving the teenagers in shock. Fortunately, Joseph had possession of the bus keys, which gives Bess the opportunity to retrieve them despite the chaos.
In the midst of this horror, Pedro forces Reggie to start the bus with a gun pressed to his head. Reggie attempts to comply but manages to wrestle the gun away briefly, leading him outside to confront the creature. Sadly, the monster sneaks up on him and rips off his head, adding to the group's grief and fear. The creature then tears out the wiring of the bus and boards it, but the teenagers manage a narrow escape. They realize that the creature appears sensitive to light, and their priority shifts to turning the tunnel's lights back on to weaken it.
While Nolan, played by Jack Kane, and Bess venture to find the main generator, the other three remain inside the bus to keep watch. During this search, Nolan uncovers evidence that suggests someone else previously knew about the creature and had attempted to kill it—photos, journals, and detailed drawings indicating a man obsessed with exterminating the beast. This man, Giulio Sarpi, was the boy seen in the opening scene, and he spent forty years studying the creature only to be killed by it. His dead body is discovered by the teens. Driven by this revelation, the group resolves to eliminate the monster themselves.
Meanwhile, Queenie asks Reggie to accompany her to the bathroom. During this moment, the creature captures Queenie, and Reggie, along with Karl, rush to fight it off. The teens use torches to fend off the beast and rescue Queenie before her wound becomes critical. The creature retaliates by attacking Reggie, almost killing him, until Nolan and Bess manage to activate the tunnel's lights, scaring it away. With their new evidence in hand, Nolan, Bess, Reggie, Karl, and Queenie plan their attack, ultimately luring the creature outside where it is now daytime. Using torches and setting the beast on fire, they trap and kill it, ending its reign of terror.
Afterward, the teenagers walk into town, feeling victorious and more connected than ever. Their narrations reveal that the answer to Joseph’s riddle was courage—a fitting reflection of what it took for them to face the danger and survive. In a chilling closing scene, authorities investigate the tunnel. A detective enters with a flashlight, but the light flickers out suddenly. The creature’s croaking and rattling sounds are heard, and it appears behind the detective, hinting that the threat may not be entirely over.
This movie blends suspense, horror, and an underlying theme of bravery, all set against the eerie backdrop of a forest and a dark tunnel. It explores how unexpected dangers can emerge from the darkness and the importance of courage in overcoming terrifying odds.
