USS Palomino, Capt. Dan Holland commanding, is on its way home after five years of fruitless searching for intelligent non-human life, when its crew determines that it must make an unscheduled course correction. Navigator Alex Durant asks the ship's robot crewman, Vincent, for confirmation. Vincent gives it, and then reveals the reason why: a black hole close aboard to port, the largest in recent history. Then Vincent reveals something else: an apparently derelict ship standing off from the black hole and somehow able to keep station, when it almost certainly should have been sucked in. XO Charles Pizer and correpondent Harry Booth are more shocked to see a ship so far from home (when the Palomino should have been the first ship to reach this deep in space) than they are to see the black hole. Vincent identifies the ship as USS Cygnus, Hans Reinhardt commanding, which disappeared twenty 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, was the father of Dr. Kate McCrae, Palomino's medical officer and ESP specialist, who maintains a telepathic rapport with Vincent and thus can communicate with him without the aid of voder, vocoder, or radio.
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 Charlie Pizer, disembark. They enter a vestibule, where automatic laser fire destroys all their hand weapons and disarms Vincent's built-in lasers, but causes no permanent injury to anyone. 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 robots commanded by an oxblood-colored levitating war machine who wordlessly challenges Vincent to a face-off. Before the two robots can go into combat, a voice interrupts them. It is Hans Reinhardt, captain of Cygnus, who introduces the war machine as Maximilian, his cybernetic master-at-arms.
Reinhardt says that he is the only human aboard, that his XO, Frank McCrae, is dead, and that the rest of the crew left Cygnus in an attempt to reach Earth (and of course, were never seen again). He states that Cygnus was disabled by a meteor storm but has since been repaired. 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 "sentry robots" brings in Charlie Pizer, apparently under arrest. Reinhardt smooths the situation over and then offers to provide spare parts for Palomino. But as Pizer and Vincent take charge of requisitioning the parts they need, Holland and Booth discover some inconsistencies in Reinhardt's story. Holland happens upon several of the apparent robots--not the gangly, ungainly sentry robots, but the much more polished robots that operate the ship's systems--conducting what looks like a funeral for one of their own. Added to this, Holland finds crew quarters still containing furnishings and uniforms, a finding totally inconsistent with a wholesale abandonment of the ship. Elsewhere, Harry Booth discovers the ship's on-board garden--which is as big as a jungle and easily "big enough to feed an army." 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, Alex and Kate are curious about Reinhardt's black-hole reconnaissance plans.
Reinhardt invites the crew to dinner. Vincent alone does not participate, but hangs out in a shooting gallery with Bob, an antique sanitation robot, and several sentry robots, led by their prototype, named Star, who had been the master-at-arms until Reinhardt built Maximilian. 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, and not only wins but manages to damage Star very badly. Bob, impressed, asks Vincent to meet him in the parts-storage bay.
There, as Reinhardt entertains the crew of Palomino and describes his black-hole reconnaissance plans, Bob tells Vincent the real story: that the smooth-walking, clothed robots are not robots at all, but are in fact the crew of Cygnus, reduced to robotic 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 (Bob has rearmed Vincent's built-in lasers) and hide the evidence. They then rejoin Holland, Pizer, and Booth, who have returned to Palomino while Alex and Kate 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 received, Frank McCrae attempted to relieve Reinhardt of his command, and Reinhardt accused McCrae of making a 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."
Holland orders Vincent to use his ESP to contact Kate McCrae, order her to return to Palomino with or without Alex, and to "tell her why." With the result that Kate tells Alex that Reinhardt is a murderer, and that the apparent robots who are running the tower-cab systems are really the crew. Alex tests this by removing the faceplate from a crewman, revealing his human face beneath. Kate is nauseated at the sight--and then Maximilian breaks off from his post and summarily executes Alex. Reinhardt scolds Maximilian, who nevertheless returns to his post. Reinhardt then appeals to Kate to somehow "protect him from Maximilian"--whereupon Kate 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 Kate taken by force to sick bay to be leukotomized. Aboard Palomino, Vincent tells Holland that Alex is dead and Kate is being taken to sick bay. Holland, Vincent, and Bob then rush to the Cygnus' sick bay, rescue Kate, and destroy half a platoon of sentry robots in a pitched battle, to the horror of Reinhardt, who watches on a monitor. Reinhardt then gives orders to let Palomino take off and then destroy it at a distance, while he continues to prepare to dive into the black hole.
Aboard Palomino, Pizer and Booth attempt to assist Holland, when Booth feigns an injury so that Pizer will leave him alone. Booth then tries to take off in Palomino, but of course gets blown up--but Palomino then crashes into Cygnus in a near-miss that causes some minor, but critical, damage. Then a hailstorm of meteors does even more damage as Vincent, Bob, Holland, Pizer and Kate McCrae now race to the probe ship that Reinhardt had earlier sent out to reconnoiter the event horizon. They must dodge a 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. Then a seven-foot video monitor tears loose from its fastenings and crashes to the deck, pinning Reinhardt beneath it. And in a hint of the poetic justice that he will eventually receive, Reinhardt cries out for help, first to Maximilian, who 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 and deals Bob a fatal "wound." Vincent clashes with Maximilian, giving Holland, Pizer, and McCrae time to board the probe ship. Then Vincent finally has the battle with Maximilian that he has always wanted to have. In the end, Maximilian tries to electrocute Vincent, who responds by using some cutting armatures of his own to rip out Maximilian's insides and send 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. But Vincent soon realizes that the ship has been programmed to follow the course that Reinhardt had set for it: a straight dive down the 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 vortex. 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.
Suddenly the viewpoint shifts to Reinhardt, floating out of control 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. That this figure is Jesus Christ is a perhaps reasonable assumption, though this is never made clear. Next, the viewpoint picks up the probe ship, now heading toward the viewer and out of a nebula. Aboard, Holland, Pizer, McCrae and Vincent awaken from an apparent trance and realize that they are headed toward a bright light--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 the portal of heaven. And on this hopeful note, the film ends.
