Test pilot Fred Norwood is flying the experimental X-109 (actually a Lockheed F-104 Starfighter) jet aircraft along with his chase plane. During the flight testing, Norwood finds himself pursued by a flying saucer and has to engage in a tricky series of aerobatics to protect his aircraft.

Once on the ground Norwood is informed that the radar tracking of his aircraft picked up no other craft near him except his own chase plane. Though Norwood insists on what he saw his superiors who have monitored his vital signs think he has had a series of hallucinations and order him off the project. Blanchard, the USAF pilot of the chase plane comes out of a room in an unusual frightened and nervous state and parrots lines about not seeing another aircraft; the event was merely an aerial inversion. When Blanchard falters with his explanation he is prompted of what to say by members of the panel in the room.

Angered and determined, Norwood decides to prove what he saw by patrolling the area in a North American P-51 Mustang equipped with laser radar until the point of exhaustion. As Norwood sleeps, his best friend Joe Vetry, a fellow pilot who is married to Norwood’s sister Dorothy takes off in the Mustang when radar picks up an unidentified flying object. Norwood and Dorothy view Joe’s aircraft vanish off the screen; later Federal Aviation Administration crash investigators tell Norwood that their opinion is his friend’s Mustang disintegrated in midair in a manner similar to some accounts of the Mantell UFO incident.

Norwood finds himself summoned to Washington D.C. where Hank Peters, a member of an influential unnamed agency of the United States Government not only believes his account but shows him a sketch that Norwood identifies as the same craft that buzzed his aircraft. Peters tells Norwood that the sketch was provided from intelligence sources based in Red China. Due to Norwood’s familiarity with a variety of aircraft, he is asked if he will accompany Peters and two scientists who will be parachuted into Red China. Peters informs him there are reliable sources that say two humanoids escaped the craft but later died, probably through exposure to the Earth’s bacteria. Due to their rapid deterioration, their bodies were cremated.

At the drop zone they are met by Chinese American agent Sam Archibald who leads them to the craft that is hidden in the ruins of a Catholic Church. Due to the Communists destroying the church, the local population will assist the Americans in any way possible. On travelling to their destination and evading units of the People’s Liberation Army they come across a party of Russian scientists led by their own version of Agent Peters. The two parties cooperate in investigating the craft.

https://en.m.wikipedia.org/wiki/The_Bamboo_Saucer