In 2047, a mysterious signal from the starship Event Horizon is intercepted on Earth. The ship, which had vanished into oblivion beyond Neptune in 2040, was deemed the most disastrous loss in space travel history. Now, it has resurfaced in a deteriorating orbit around Neptune, prompting the dispatch of the Lewis and Clark, a rescue vessel. This crew is under the command of Capt. Miller and includes the Event Horizon's creator, Dr. William Weir.
Upon their arrival, the crew learns from Dr. Weir that the Event Horizon was designed to test an experimental gravity drive, intended to generate an artificial black hole. This would theoretically connect two points in space, greatly shortening travel times. The ship was on its inaugural test run to Proxima Centauri when it mysteriously disappeared. The only signal received since its return is a chilling recording from Capt. Kilpack, containing a series of agonizing screams, including the Latin plea, liberate me ("save me").
As the Lewis and Clark approaches the derelict spaceship, the crew finds no clear sign of life onboard. Confounding sensor readings compel them to enter the Event Horizon to look for survivors. Inside, they quickly split up—the Medical Tech Peters discovers a frozen human corpse, unsettlingly devoid of its eyes. Meanwhile, Engineer Justin stumbles upon a disturbing black mirror within the ship's core, leading to a traumatic encounter that leaves him catatonic.
With their ship critically damaged and only 20 hours of breathable oxygen available, the remaining crew members reluctantly relocate to the Event Horizon. Shortly thereafter, Justin, having emerged from his stupor, attempts to escape the haunting memories by ejecting himself into space but is salvaged by Miller, albeit with serious injuries.
As time unfolds, the crew begins to experience harrowing hallucinations stemming from their deepest fears and regrets. Miller is haunted by visions of a colleague he was unable to save during a fire, while Peters confronts traumatic memories of her son, Denny. The tortured widower, Dr. Weir, visions of his wife, Claire, who appears missing her eyes, urging him to join her.
The crew soon uncovers that the Event Horizon's drive did achieve its goal of bending space-time, albeit leading into a dimension of "pure chaos" and "pure evil." A reconstructed video log reveals the original crew engaged in unthinkable acts of violence and depravity immediately after activating the gravity drive. The previously heard Latin message is clarified as Liberate Tutame Ex Inferis ("save yourself from Hell").
It becomes evident that the Event Horizon has returned with insidious intent, targeting the crew's personal traumas to drive them towards this chaotic dimension. As repairs on the Lewis and Clark continue, Miller resolves to destroy the Event Horizon, despite Dr. Weir's vehement protests. Tragic occurrences follow, including Peters meeting her demise as she is lured to her death by the apparition of her son.
Dr. Weir abandons the crew, and after discovering Peters' body, he is compelled by a horrific vision of his wife's suicide, leading him to inflict violence upon himself. In a twisted turn of events, Weir detonates explosives on the Event Horizon, killing the pilot Smith and sending rescue Tech Cooper hurtling into the void of space. Seemingly under the influence of the ship's malevolent force, Weir threatens the remaining crew with a nail gun, asserting that the ship is "alive" and will not permit any escape.
With the gravity drive now activated, a countdown commences, bringing the Event Horizon towards its descent back to the chaos dimension. Cooper, utilizing his space suit's oxygen, successfully maneuvers back to the ship and inadvertently causes Weir to shoot out a bridge window, sending him spiraling into the blackness of space.
In a climactic confrontation, Miller struggles against the fiery specter of his former comrade while making his way to the explosives. Inside the ship's core, a grotesque transformation of Dr. Weir attempts to deter him, as visions of the crew's harrowing fates flash before his eyes. However, Miller manages to reach the detonator, sacrificing himself and triggering the ship's destruction. The Event Horizon detonates, severing its structure, while the remaining crew members—Starck and Cooper, alongside a comatose Justin—find refuge in the surviving forward decks and prepare for stasis.
As Starck dreams of a disfigured Dr. Weir's rescue, she awakens to an unsettling reality—distressed by the true rescuers who arrive too late. Cooper restrains Starck amidst the chaos as the automated hatch to their stasis chamber seals shut, leaving an ominous suggestion that the dark presence aboard the Event Horizon persists, independent of its chaotic drive.
