The story takes place at Los Alamos, New Mexico, where a nuclear physicist (Barry) lives and works.

The film was nominated for an Academy Award for Best Writing (Story and Screenplay), Sydney Boehm being the nominee.

They have a young son, Tommy, who goes with school mates to Santa Fe for a carnival with their teacher, Ellen Haskell.

When a kidnapper instructs Frank to steal a file from the atomic lab and mail it to a Los Angeles hotel, he wants to inform the authorities, but Martha fears for their boy.

A small-time thief, David Rogers, collects an envelope with the file at a post office, but they alert the FBI who follow him.

Watching the film footage the FBI spots a hot-dog vendor who is actually Donald Clark, a man with Communist ties.

Tommy is moved by kidnappers to the Puye Cliff Dwellings in New Mexico, where they briefly encounter the Fentons, a family of tourists.