Jim Hollenbeck (Guy Madison), a dedicated physician assigned to the space branch of the United States Air Force Medical Corps, voluntarily undergoes jump school training.

After jump school, Lt. Col. Masters (Walter Coy), the head of the space program, sends Jim to Sovern Air Force Base in Florida to evaluate a problematic experimental ejection seat.

Before accepting the assignment, Jim asks his fiancée, Pat Lange (Virginia Leith), for her blessing and the couple marry but their honeymoon is cut short by the news that Col. Masters was killed in an automobile accident.

Reaching 100,000 feet (30,000 m), his radio fails, and when he drifts over a rugged mountain range, Jim discovers that his oxygen is nearly gone, forcing him to land.

Nine tests were conducted of the seat from a B-47 over Eglin's water ranges over the Gulf of Mexico, by the Air Proving Ground, at an altitude of 10,000 feet and various speeds.

[6] "Actually, we feel that the star of the movie will be the Air Force and the progress it is making in the aero medical field," said Robert Webb, director, in commenting on the film.

"A crew consisting of 79 members including technicians and cast, of 20th Century Fox Film Corporation" shot in the Eglin / Fort Walton Beach area for about seven days, starting on September 15.

A. M. Weiler noted: "Colorful proof that science can be stranger and more interesting than science-fiction is presented in 'On the Threshold of Space,' which landed at the Globe yesterday.