In the year 2130, the deep space research ship USS Palomino is on a search for intelligent non-human life on other planets. The crew is comprised of Captain Dan Holland (Robert Forster
), Lt. Charles Pizer - the hotshot first officer (Joseph Bottoms
); utility droid LF#396, informally known as VINCENT (voice of Roddy McDowall
); Dr. Alex Durant (Anthony Perkins
) - navigator and science officer; Dr. Kate McCrae (Yvette Mimieux
) - medical officer and empath, who maintains a telepathic rapport with VINCENT via her ESP; and embedded journalist Harry Booth (Ernest Borgnine
). After five years of fruitless searching, the Palomino is now on her way home for a refit when VINCENT notices a large, swirling blue accretion disk and recommends a course correction. VINCENT identifies the disk as a black hole, the largest discovered in recent history. While the crew nervously discuss the destructive potential of black holes, VINCENT reveals something else: an apparently derelict ship standing off from the black hole's event horizon (line of no return) and somehow able to keep station, when it almost certainly should have been sucked in. Pizer and Booth are more shocked to see a ship so far from home (when the Palomino should have been the first spaceship to reach this deep in space) than they are to see the black hole. VINCENT identifies the ship as USS Cygnus, with the German scientist Hans Reinhardt (Maximilian Schell
) commanding, which disappeared nearly 20 years earlier after apparently failing to heed recall orders after its mission, the same as Palomino's, was declared a failure. (In addition, Booth remembers Reinhardt as arrogant, pompous, and utterly heedless of the value of taxpayers' money.) The Cygnus, however, holds another significance for the crew of Palomino: its XO, Frank McCrae, is Kate's father.
Against his better judgment, Holland accepts the recommendations of Pizer and Durant and comes about to rendezvous with Cygnus. As they approach, they come under the influence of the black hole's tremendous gravity. But at their closest approach, the gravity ceases. Durant speculates that something from the Cygnus is responsible, but no one aboard can decide what that might be. Then Palomino falls away from Cygnus and is very nearly sucked into the black hole. Palomino escapes but is badly damaged and now needs spare parts. So when Palomino once again comes under the apparent protective influence of Cygnus, the crew start to look for a way to board--when suddenly Cygnus blazes with light, as if to welcome them.
Palomino docks with Cygnus, and the crew, except for Lt. Pizer, disembark. They enter a vestibule, where automatic laser fire destroys their guns and knocks out VINCENT, he is not seriously damaged, but his combat protocols are now offline. Holland radios Pizer, telling them they have been disarmed, but uninjured, before the crew moves forward. Then they board an automatic cart, part of a ship-wide transportation system, and ride in comfort to Cygnus' conning tower. They ride a hoist to the tower cab, which they find occupied apparently by a crew of "humanoids" with hooded robes and mirrored faceplates. Though the humanoids ignore them, they do get the attention of an oxblood-colored levitating war machine who wordlessly challenges VINCENT to a face-off. Before the two robots can go into combat, Dr. Reinhardt emerges from the shadows and orders them to stand down. He identifies the war machine as Maximilian, his cybernetic master-at-arms.
Reinhardt says that he is the only human aboard. Cygnus was disabled by a meteor storm, he and Frank McCrae stayed behind to make repairs while the rest of the crew left Cygnus in an attempt to reach Earth (and of course, were never seen again). The elder McCrae has since passed on. He also admits, or rather avows, that he refused to obey his recall orders, because he proposes to reconnoiter the black hole--and pilot his ship "in, through, and beyond" it, to another dimension that he is sure exists.
Their conversation is interrupted when a squad of armored "sentry robots" brings in Pizer, apparently under arrest. Reinhardt smooths the situation over and then offers to provide spare parts for the Palomino. Pizer and VINCENT take charge of requisitioning the parts they need, and they meet LF#28, informally known as BOB, (voice of Slim Pickens
), an old rusted sanitation droid who has languished since the human crew's disappearance.
A little later, Holland happens upon several of the humanoids conducting what looks like a funeral for one of their own. He also finds crew quarters still containing furnishings and uniforms, a finding totally inconsistent with a wholesale abandonment of the ship. Elsewhere, Booth discovers the ship's on-board garden--which is as big as a jungle and easily "big enough to feed an army," and notes that its mute groundskeeper is sporting a notable limp. The crew of Palomino reassemble to discuss what they have seen--and while Holland very much wants to accept the spare parts and depart from Cygnus as rapidly as possible, Durant and McCrae are curious about Reinhardt's black-hole reconnaissance plans. Reinhardt launches an experimental probe-ship to reconnoiter the black hole's event horizon, then invites the Palomino crew to a dinner party, where he will explain his research.
While Reinhardt entertains the Palomino crew in his spacious, Victorian inspired dining hall, VINCENT hangs out in a shooting gallery with BOB and several sentry robots, led by their prototype, Captain STAR. BOB explains that STAR had been the master-at-arms until Reinhardt built Maximilian, and is also responsible for much of the abuse BOB has endured over the years. STAR challenges BOB to a shooting match, and wins only because he had distracted BOB by bumping him as he was shooting. BOB then confesses that he let STAR win on purpose, to avoid retaliation. Outraged, VINCENT challenges STAR to a match. Though STAR again cheats, VINCENT still manages to beat him, and STAR is so angered by his defeat that he ends up literally blowing a fuse. BOB, impressed, asks VINCENT to meet him in the parts-storage bay.
Inside the dining hall, Reinhardt is eagerly discussing his research with his new guests. Eventually, Maximilian notifies him that the probe-ship has returned, and Reinhardt excuses himself to debrief the pilot. After he has left, Holland and Booth discuss the inconsistencies they have discovered in Reinhardt's story. Holland and Booth are now convinced that Reinhardt is insane, but Durant wants to give him the benefit of the doubt.
Now able to speak freely, BOB restores VINCENT's combat protocols to 100%, and tells him the real story: the humanoids are not robots at all, but are in fact the crew of Cygnus, reduced to drone-like mentality by a series of laser prefrontal leukotomies. As the two robots are reconnoitering the sick bay where some maintenance leukotomies are taking place, two sentry robots discover them. VINCENT and BOB destroy them and hide the evidence. They then rejoin Holland, Pizer, and Booth, who have returned to Palomino while Durant and McCrae have remained in the conning tower cab with Reinhardt. BOB tells the three men what really happened to the crew: that when the recall order was refused, Frank McCrae attempted to relieve Reinhardt of his command, and Reinhardt accused Mr. McCrae of mutiny and then killed him. He then had his sentry robots capture the rest of the crew and subject them to the prefrontal leukotomies that have turned them into "humanoid robots." Meanwhile, Reinhardt and Maximilan discover the remains of the two sentry robots BOB and VINCENT were forced to destroy, and decide that it is now time to "liquidate" their guests.
Holland orders VINCENT to use his ESP to contact McCrae and order her to return to Palomino with or without Durant, and to "tell her why." With that result, McCrae tells Durant that Reinhardt is a murderer, and that the apparent robots who are running the tower-cab systems are really the original crew. Durant tests this by removing the faceplate from a crewman, revealing his human face beneath. McCrae is nauseated at the sight--and then Maximilian breaks off from his post and summarily executes Durant. Reinhardt scolds Maximilian, who nevertheless returns to his post. Reinhardt then appeals to McCrae to somehow "protect him from Maximilian"--whereupon McCrae denounces him to his face and says, "If there is any justice at all, the black hole will be your grave!"
As a rejoinder, Reinhardt orders McCrae taken by force to sick bay to be leukotomized. Aboard Palomino, VINCENT tells Holland that Durant is dead and McCrae is being taken to sick bay. Holland, VINCENT, and BOB then rush to the Cygnus' sick bay, rescue McCrae, and destroy half a platoon of sentry robots in a pitched battle, to the horror of Reinhardt, who watches on a video monitor. Reinhardt orders the sentry robots to terminate any unauthorized humanoids on that section of the ship, then instructs Maximilian to let Palomino take off and then destroy it at a distance with the Cygnus lasor cannons, while he continues to prepare to dive into the black hole.
When the allotted time passes, Booth is eager to write off Holland and McCrae as dead and leave. Pizer refuses, insisting on a rescue attempt. Succumbing to cowardice, Booth feigns an injury so that Pizer will let him return to the ship. Holland, McCrae, and the droids find themselves pinned down by sentry robots as they get closer to the Palomino, but Pizer, armed with twin pistols, manages to outflank the attackers. Booth then tries to take off in the Palomino alone. Endangering the Cygnus and himself due to his poor piloting skills, he nearly hits the conning tower before Cygnus' lasor guns shoot him down--but Palomino then crashes into Cygnus in a near-miss that causes some minor, but critical, damage. The Palomino crew now have only one avenue of escape: the probe-ship.
As the Cygnus gets closer to the accretion disk, it is pulverized by a hailstorm of meteors, severely compromizing its hull and taking its emergency reactors and null gravity generators offline. The Palomino survivors must dodge a large, red-hot meteor that crashes into the ship and traverses the entire main corridor, and pass through the ship's garden after it, too, is breached, all the while dodging and battling sentry robots.
In the conning tower cab, the humanoid crew receive alarming signs that the ship is now subject to structural overload. Reinhardt orders Maximilian to prepare the probe-ship for launch. As Maxmilian starts to leave, a seven-foot video monitor tears loose from its fastenings and crashes to the deck, pinning Reinhardt beneath it. In a hint of the poetic justice that he will eventually receive, Reinhardt cries out for help, first to Maximilian, who apparently deserts him to make his/its own escape in the probe-ship, and then to his leukotomized crew, who of course cannot begin to understand him now.
Maximilian reaches the probe-ship docking hoist first and ambushes the surviving Palmonino crew. After BOB is taken offline and Pizer is knocked out, VINCENT attacks Maximilian, giving Holland, Pizer, and McCrae time to board the probe-ship. VINCENT and Maximilian fight using every gadget at their disposal, culminating with Maximilian catching VINCENT in a bear hug-like grab and attempting to electocute him. VINCENT responds by using his cutting armatures to disable Maximilian's antigravity stabilizers, which sends him spinning out of control through a hull breach and into the black hole.
BOB, too weak to function any longer, says his goodbyes to VINCENT, who then reluctantly abandons BOB and boards the probe-ship. Holland lifts off as the Cygnus, now twisted into a lump beyond all recognition, is caught up in the whirlwind of stellar detritus that surrounds the black hole. Holland tries to set a course away from the black hole, but nothing responds. VINCENT soon realizes that the ship has been programmed to follow the course that Reinhardt had set for it: a straight dive down the vortex funnel of the black hole. Unable to alter that course, the three humans decide to "pray that Reinhardt was a genius."
And so the probe-ship takes its straight dive down the black-red vortex and into the black hole. As it does, the crew start to hear voices--Reinhardt's and their own--repeating words spoken long ago, an effect of the tremendous time dilation as space-time is bended.
Suddenly the viewpoint shifts to Reinhardt, floating out of control in the reddish vortex of the black hole in the same pose that he assumed when the seven-foot monitor in the tower cab crushed him. Then he catches up with Maximilian--or rather, Maximilian, who has been waiting for him, now takes him in an unbreakable embrace and draws him closer--until Reinhardt becomes Maximilian, which the viewer realizes because Maximilian's charged-coupler optical device is now a simple visor, out of which Reinhardt's frightened eyes suddenly stare. Worse yet, Reinhardt/Maximilian finds himself standing on a basalt promontory over a fire-covered craggy landscape, accompanied by his leukotomized crew. As the view withdraws from Reinhardt/Maximilian and pans down and then forward to show Cygnus' crew and then the fiery lake behind them, the viewer realizes that they are all, quite simply, in hell.
Then a church-window-shaped portal opens, and the viewpoint rushes through it and through an arched corridor, through which a robed figure, arms outstretched, floats past the viewer and forward. Next, the viewpoint picks up on the probe-ship, now heading toward the viewer and out of a nebula-like star. Aboard, Holland, Pizer, McCrae, and VINCENT awaken from an apparent trance and realize that they are headed toward a bright light in space--not the harsh, lethal light of a star, but a very pleasant, warm light. They sit back and let the probe ship take them toward the light--which is apparently a white hole: the portal of heaven. The so-called four survivors of the USS Palomino have put the black hole behind them forever. And on this hopeful note, the film comes to a close.