Dr. Malcolm Betruger [Dominic Mafham] leads a bold teleportation experiment at a United Aerospace Corporation (UAC) outpost on Phobos, using ancient gateways known as Gates to shuttle a volunteer from a Nevada lab. The test looks promising at first, but the subject arrives fractured in body and mind, a troubling omen of the Gate’s unpredictable power. Back on a transport vessel, a squad of marines rouses from cryosleep to guard the Phobos base. Among them is Joan Dark [Amy Manson], a disgraced lieutenant whose reputation precedes her, and Bennett Stone [Luke Allen-Gale], a scientist who shares a complicated history with her. Despite Dr. Ahmed Kahn’s warnings, Betruger pushes ahead, hoping to teleport himself to the Nevada facility. After a careful cascade of medical steps led by Veronica, Betruger steps through the Gate, and almost immediately the Phobos base shutters offline as monstrous forces spill out.
The marines must press forward without the usual lines of communication or a direct path into the base. They slip inside through an emergency entrance, where Bennett discovers the reserve power has plummeted to two percent. Time is of the essence: only about ninety minutes remain before the fusion reactor reaches a critical meltdown. The team is immediately beset by corrupted UAC staff transformed into zombie-like beings, turning the once routine guarding mission into a life-or-death scramble. In the chaos, they stumble upon three survivors: Betruger, Veronica, and the base’s Chaplain, Glover, setting the stage for a clash of ideologies. Betruger argues that the Gates are a long-sought tool for planetary colonization, while Glover believes the Gates are demonic in nature. Against Betruger’s wishes, Joan orders the remaining Marines and the survivors to evacuate the base to preserve the possibility of a future.
Back on the transport, the crew is ambushed by Imp-like demons that tear through the hull, taking down several marines and eliminating Glover in the process. With the transport crippled, Joan reluctantly agrees to Betruger’s plan to restore power so they can use the Gate to teleport the survivors to the Nevada base. Yet she ensures Bennett understands that this is all part of a broader plan to reestablish communications, a ruse to reach the outside world. As Bennett works to restore power, Betruger drops a brutal truth: Joan was disgraced for her role in letting a terrorist go free, a past mistake that haunts her. Betruger wastes no time in furthering his own schemes, killing Veronica and sealing the marines inside the power server as the Imps close in.
Only Joan and Bennett remain standing, and the two of them realize they must stop Betruger from activating the Gate. Joan seizes the infamous BFG 9000 and fights her way toward the Gate chamber, a desperate bid to end the threat. The confrontation intensifies when Bennett is dragged down by an Imp, and Joan is forced to press on alone. In a brutal turn, a zombified Bennett confronts Joan, compelling her to shoot him to stop him from becoming another weapon in Betruger’s hands. She then guns down Betruger, who resurrects instantly and drives Joan into the Gate itself.
Joan is hurled into at hell, where a grotesque horde of Imps and their overlord Stanga await. Stanga reveals their plan to reclaim Earth and wipe humanity from the face of the planet. Braving the infernal landscape, Joan fires plasma grenades and uses every resource at her disposal to scatter the demonic tide, inching her way back toward an exit that will return her to the Nevada base. When she reemerges, she demands that the Gate be shut down, a direct challenge to Betruger’s ambitions. Security apprehends her and she is sedated, seemingly defeated, as the Gate begins to stir once more. Dr. Kahn’s assessment lingers in the air, convinced that Betruger is attempting to slip through once again, and the film cuts to black with only a menacing growl breaking the silence, leaving the ultimate fate of the Gate and humanity uncertain.
