Lieutenant Berton, Guy Davis, a Canadian tunneller on the Western Front in 1918, digs 78 feet (24 m) beneath a German position to rescue fellow tunnellers, and the startled screams of a survivor reverberate upward, alerting the German defenders above. When the German charges detonate, Berton is suddenly trapped underground for twelve days, facing a claustrophobic silence broken only by distant sounds and flickers of hope.
On November 2, 1918, three months after Berton’s entombment, Major Jennings and Dr. Priest of the British Army Intelligence Corps brief Colonel Ashcroft about a deep underground German bunker known as “Trench 11,” hidden in the Argonne Forest—almost eleven miles behind the front lines. The Germans had called it the Wotan Complex, and it is suspected to be a hidden base where Reiner, a formidable officer nicknamed “The Prophet” by his men, continues to refine chemical and biological weapons. The Allied plan is to confirm whether Trench 11 still serves as a launch point for these weapons, and Colonel Ashcroft orders U.S. troops to accompany Jennings, Priest and Berton as they descend into the cratered earth to investigate. Berton, who has begun a fragile romance with a French woman named Veronique, is pulled away from a brief leave to join the mission. The team—Captain Cooper, Sergeant Pronger, and Private Kelly alongside Jennings, Priest and Berton—press deeper into the bunker and encounter the grim aftermath of a German retreat as comrades lie dead in the trenches.
Inside the German headquarters, Reiner and Captain Mueller receive orders to erase traces of the operation at Trench 11. Reiner had failed to detonate the explosives that would have erased any clues, and Mueller, uneasy with Reiner’s methods, is tasked with guiding him back to the bunker to ensure its destruction. The investigators uncover evidence of German infighting and sabotage, eventually stumbling upon a sealed lower level. A German soldier left behind pleads with the group not to open the door, but his warnings go unheeded and Cooper shoots the terrified man when he becomes hysterical.
As they press forward, the group is assaulted by a series of threats: a crazed occupant in a hospital-like room and a disturbing emergence—a worm that crawls out from a gunshot wound after a death. Dr. Priest studies the corpse and concludes the creatures are engineered parasites that have jumped species to infect humans. The worms, designed to target livestock, have evolved to threaten people as well, and Reiner’s enthusiasm for their potential destruction fuels a brutal resolve.
Tensions rise as Pronger and Kelly press to leave, prompting a standoff with Jennings. The escape attempt is interrupted by an assault from infected soldiers who kill Pronger and capture Kelly and Dr. Priest. Berton and Cooper stumble upon an exit but are themselves captured. Mueller, having already lost a tunneller to the infected, struggles to reinstate the charges and convince the prisoners to help. Dr. Priest refuses to cooperate, choosing humanity over blind obedience. Kelly’s health deteriorates under the parasite’s control, and Reiner interrogates Priest about sparing civilian lives, only to dismiss any mercy as he pushes toward his broader ambitions.
Mueller discovers the demolition charges were never connected to a timer, and Reiner begins sealing the lower level while harvesting more parasites. The group escapes long enough for Berton and Mueller to attempt a remote detonation, but an infected attacker shatters their plan, breaking Mueller’s leg and destroying the timer. With time against them, Berton endures torture and distraction at Reiner’s hands as Mueller fights to secure a working bomb. The final assault culminates in a chaotic clash around the charges: Berton detonates the explosives, triggering a collapse that buys him passage to safety. In the aftermath, Reiner falls victim to the turmoil as a vial pierces his eye and the tunnel collapses around him. Berton, battered but alive, staggers away and is haunted by a vision of Veronique as the smoke and dust settle.
