WHEN WORLDS COLLIDE

In the prologue, quotes from the Book of Genesis are shown and narrated, describing God's decision to wipe out humanity.

Pilot David Randall flies top-secret photographs from South African astronomer Dr. Emery Bronson to Dr. Cole Hendron in the United States. Hendron, with the assistance of his daughter Joyce, confirms their worst fears: Bronson has discovered a rogue star named Bellus, accompanied by an Earth-sized planet named Zyra, which is on a collision course with Earth.

Hendron warns the United Nations that the end of the world is little more than eight months away, with a close pass first by Zyra, before Bellus destroys the Earth nineteen days later. He pleads for the construction of "arks" to transport a lucky few to Zyra in the faint hope that humanity can be saved from extinction. With other scientists scoffing at his claims, his proposal is rejected.

Two wealthy humanitarians arrange for a start to construction and a lease on a former Army proving ground to build an ark. To finance the rest, Hendron meets with wheelchair-using business magnate Sidney Stanton. Stanton demands the right to select the passengers in exchange for his money, but Hendron insists that he is not qualified to make those choices; all he can do is buy a seat on the ark. Stanton capitulates. Groups in other nations start building their own spaceships.

Joyce tells her father she is attracted to Randall, so he finds an excuse to keep him around, much to the annoyance of her longtime boyfriend, medical doctor Tony Drake. As Bellus nears, martial law is declared and residents in coastal regions are relocated inland.

Zyra makes a close approach first, causing massive earthquakes, volcanic eruptions, and tsunamis that wreak havoc around the world. Dr. Bronson is killed by a falling crane. Afterward, Drake and Randall travel by helicopter to drop off supplies to people in distress. When Randall gets off to rescue a little boy stranded on a rooftop in a flooded area, Drake flies away with the boy, leaving Randall stranded, but reconsiders and returns.

As the day of doom approaches, the passengers are selected by lottery, though Hendron reserves seats for himself, Stanton, Joyce, Drake, pilot Dr. George Frey, and Randall, for his daughter's sake. He also includes the young boy who was rescued, for a total of 45 passengers. Randall, feeling he lacks any needed skills, rejects his guaranteed seat and instead pretends to draw a lottery number, but Hendron knows better. For Joyce's sake, Drake later tells Randall that Frey has a "heart condition" that may kill him during liftoff, convincing Randall he is needed as co-pilot.

The cynical Stanton fears what the desperate lottery losers will do, so he stockpiles weapons. When a young man turns in his winning number because his sweetheart was not selected, Ferris – Stanton's longsuffering assistant – claims it at gunpoint, but is shot dead by Stanton. Hendron adds the young woman to the passenger list, over Stanton's objections, and takes the precaution of having the chosen women board the ark while the men wait outside. Shortly before liftoff, many of the lottery losers seize Stanton's firearms to try to force their way aboard. Hendron initiates the launch prematurely, while he and Stanton are still outside, to conserve fuel and improve the chance of a successful landing. With an effort born of ultimate desperation, Stanton stands up and walks in a futile attempt to board the departing spaceship.

The crew are rendered unconscious by the g-force of acceleration, and do not witness Earth's collision with Bellus. When Randall comes to and sees Dr. Frey already awake and piloting the ship, he realizes Drake deceived him.

After the spaceship enters Zyra's atmosphere, the fuel runs out. Randall glides the ship to a safe landing on snow. Zyra turns out to be habitable. Randall and Joyce walk hand-in-hand down the ramp with their fellow survivors as a new day dawns. In the background, an artificial structure is visible.

The chosen survivors launch in their rocket and successfully escape Earth's destruction, landing on Zyra to start anew.

The conclusion offers a vision of hope and renewal for humanity, as a small group overcomes social divisions and personal sacrifice to survive extinction. The film lands on a note of awe and uncertainty, echoing its biblical framing by suggesting that disaster can be a catalyst for rebirth—as long as we bring our better selves along for the ride.