An elite Special Ops unit, led by Captain Mack, is dispatched by Dr. Elissa Cardell, a CIA operative, to rescue her father, Lee Wesley, a scientist stranded at a desert dig suspected of concealing a bunker for weapons of mass destruction. The team lands at the arid site and quickly confronts an unsettling sight: a priest covered in boils. Their medic, Doc Harrington, administers a sedative to the man in hopes of keeping him from harming anyone. IT specialist Click powers up the elevator and uncovers a cryptic reference to the “Gehenna Project,” a term Cardell insists she does not know. Mack orders communications specialist Nickels to remain on the surface to repair gear and keep watch over the priest while the rest descend into the subterranean chambers.
Underground, the team faces Duncan, a scientist with boils like the priest who attacks with a corrosive goo and is shot dead. While treating Duncan’s wound, Doc Harrington experiences a disturbing vision of her sister accusing her of letting her die. Duncan and Doc vanish, forcing the squad to split up in a desperate search. They find Duncan attempting to pry open a sealed room; he lunges at them and is killed. The sealed room is opened from the inside by Father Fulton, a priest Cardell knows, who leads them toward the temple but then turns violent, attacking Nickels with the same acidic substance and dragging him away. On the upper floor, Click discovers Doc locked in a room and tries to free her; Hammer intervenes and rescues Click, but a growing wave of possessed scientists swarms the corridors, forcing Hammer to collapse a passage with explosives to delay them.
Back above, Cardell and Fulton reveal a stark truth: the temple is one of many tombs crafted by God to imprison the malevolent Nephilim, a force capable of possessing scientists and turning the team against one another. The mission fractures further when Yoshi stalks a hallucinatory path and encounters the now-possessed Doc, who seduces and then inhabits her. Doc’s possession dents the group’s cohesion as she lures Hammer into a dangerous standoff; Hicks tries to intervene, firing at Hammer to prevent him from shooting Doc, and the two men clash before Hicks is killed by Doc and Yoshi. The tension tightens as the team confronts the horrifying possibility that the Nephilim have found a way to control their minds.
Hammer later regroups at the temple to report his findings. Fulton divulges that the Gehenna Project is a self-destruct protocol activated, in part, by Cardell’s unintentional assistance and aided by Click’s actions. With only about fifteen minutes to evacuate, the temple’s doors begin to close. Fulton, Mack, Cardell, and Click manage to escape via the elevator, but Hammer remains trapped inside and detonates grenades to hold back the onslaught of possessed scientists, sacrificing himself in the process. Fulton makes a final dash for safety but is killed by Doc as he reaches the elevator shaft.
Mack, Cardell, and Click press onward and locate Wesley, who is possessed but lacks the tell-tale boils that marked his earlier condition. Doc, now possessed, joins the assault along with Nickels. Click is slain in the struggle, and Mack uses an explosive barrel to end Doc’s threat and disable Wesley. Cardell then faces Wesley, and, choosing a higher duty over personal ties, channels the Nephilim into herself to set his soul free, refusing to flee with Mack because saving her father was always her sole objective.
Moments before the blast, Mack escapes the dig site and is rescued by a helicopter. The mission haunts him with visions of his late friend and mentor Blakeney, a guilt-ridden memory from a past order to kill him. With these memories finally laid to rest, he embraces a new purpose: becoming a soldier in the ancient war between God and the Nephilim, a vigil aligned with the larger, timeless conflict that frames the mission’s legacy.
