Beyond the Time Barrier

In 1960, Major Bill Allison flies the X-80 to sub-orbital space but loses radio contact. He returns to an abandoned airbase and, spotting a distant futuristic city, heads toward it. He is rendered unconscious and captured by the Citadel's forces.

Allison awakens in an underground city and is brought before the Supreme. He learns that the Citadel is ruled by the Supreme and his Captain, with most residents deaf-mutes. The Supreme and Captain are the only capable speakers/hearers among the people.

The Captain sends Allison to an underground containment area where bald mutants attack. He fights them off and learns they blame the Citadel residents for a 'cosmic plague' that decimated humanity. The mutants claim to be survivors and vow vengeance.

Trirene reads Allison's thoughts telepathically and is convinced he is not a spy. She shows him historical photographs to explain the Citadel's past and leads him to the 'scapes'—two scientists and a Russian officer.

The scientists explain that Allison has traveled to the year 2024. Nuclear fallout damaged the atmosphere, allowing cosmic rays in 1971 and triggering a cosmic plague. Even underground residents were afflicted, and the 'scapes' arrive from different eras as time travelers: Markova from 1973 and Kruse and Bourman from 1994.

As they spend more time together, Allison and Trirene grow closer and fall in love. Their romance complicates the plan to navigate the Citadel's politics and the uncertain future. The bond deepens as different time travelers exist among them.

The 'scapes' begin discussing a plan to leverage Trirene's influence to persuade the Supreme and enable Allison to travel back in time. Markova steps forward, demanding that she accompany Allison to 1973 rather than 1960, complicating loyalties. The Captain warns against trusting the time travelers, while Allison weighs his options.

Kruse and Bourman arrive from different times; Bourman intends to hijack the X-80 to return to his own era, while Kruse is revealed to have his own agenda. Bourman defeats Kruse and asserts his intention to use the aircraft to reach his time horizon. The confrontation heightens the danger surrounding the plan.

During the struggle over Kruse's pistol, a stray bullet fatally wounds Trirene before Allison can overpower Bourman. The loss devastates Allison and the Citadel, destroying any immediate hope of using Trirene to repopulate their world.

Allison carries Trirene's body to the Supreme, who is distraught by his granddaughter's death and the doom of his people. He directs Allison toward a secret passage out, persuaded by Allison that there is always hope. The moment marks a fragile beacon amid the Citadel's collapse.

Returned to the present, Allison recounts his adventure in a recorded debriefing. He appears aged and is hospitalized as officials listen to his tale. He warns them about future events and passes Trirene's ring, which the Supreme had slipped onto his finger, to provide a link to the Citadel's world.