A young FBI agent assigned to guard the Lakeview Laboratory of Nuclear Physics, a top secret research facility devoted to the development of the atom bomb, is murdered. Senior government agent Daniel F. O'Hara (Dennis O'Keefe), assigned to the project, launches an intense manhunt for his killer.

Dan and other agents suspect an illegal alien, Anton Radchek (Philip Van Zandt), and trail him to a San Francisco rooming house. Radchek is murdered, after he called Igor Braun (Onslow Stevens).

At San Francisco FBI headquarters, Dan is introduced to Philip 'Scotty' Grayson (Louis Hayward), an emissary from Scotland Yard on a special mission to track down an artist who has been exporting paintings to London, which, under ultra violet light, reveal a secret formula. When Dan notices that the painting is signed by Igor Braun, the two agents join forces to find the location depicted in the painting. Tracing Braun to an apartment in the city, they discover he's completing another painting with an embedded secret formula, destined for London.

Braun flies to Los Angeles and then drives to an art shop in Lakeview owned by Adolph Mizner (Grandon Rhodes), the leader of a communist spy ring. Following Braun, Dan and Grayson then confer with Dr. Frederick Townsend (Art Baker), the director of the Lakeview project. The agents realize one of the five scientists working on the project is a traitor: Dr. Toni Neva (Louise Allbritton), Dr. Ritter Van Stolb (Carl Esmond), Dr. William Forrest (Lowell Gilmore), Dr. Homer Allen (Charles Evans) and Townsend.

Braun sends another painting to London, prompting Dan to surmise that the formula was smuggled out through the plant laundry. Posing as a worker, Grayson infiltrates the laundry and observes Toni drop off a load of clothes from which the clerk extracts a handkerchief, which he then slips into a box of men's shirts. After Krebs (Raymond Burr), one of the spies, picks up the box, Grayson knocks him unconscious, steals the box and finds a formula inscribed on the handkerchief.

Hurrying to Grayson's rooming house, the spies begin to brutalize Grayson and his landlady, Mrs. Ecko (Tamara Shayne), when Dan arrives. Dan and Grayson then overpower their captor, but in the fray, the landlady is killed.

The next day, Van Stolb's body is discovered murdered. While following Allen, one of the three remaining scientists, Dan, is shot at and forced over a cliff by Krebs. Grayson speeds to rescue Dan from his burning vehicle, and they alert the police about Allen. With the help of the police, the agents locate Allen and Braun closeted in a small house. After a blazing shootout, the agents arrest Allen, the scion of a prominent Boston family, as the traitor. When Allen proclaims his loyalty to his country, Dan forces open his palm, revealing an imprint of the secret formula.

A 1948 American Black & White anti-communist Cold War crime film directed by Gordon Douglas, produced by Edward Small and Grant Whytock, screenplay by George Bruce, story by Bertram Millhauser, cinematography by Edward Colman and George Robinson, starring Louis Hayward, Dennis O'Keefe, Louise Allbritton, Carl Esmond, Onslow Stevens, Art Baker, Lowell Gilmore, Philip Van Zandt, Charles Evans, Frank Ferguson, Reed Hadley, and Raymond Burr.

Exteriors are mostly from San Francisco but the film starts with exteriors from Brand Boulevard, Glendale, California.

The film was one of the first Cold War movies, made specifically to exploit the new anti-communist sentiment in the country after World War II. Producer Edward Smalls hoped to repeat the success he recently had with the film-noir "T-Men" (1947) and "Raw Deal" (1948). It was director Gordon Douglas' first major production; he had been making B-Movies for MGM.

The original title was "Face of Treason", which was changed to "FBI vs Scotland Yard". FBI director J. Edgar Hoover requested it be named, "FBI Meets Scotland Yard", but Small eschewed any collaboration with the agency, as he had discovered how controlling Hoover was. Hoover was involved with a big hit, "The House on 92nd Stree" (1945), a movie about the FBI's pursuit and conquest of domestic Nazis that showcased the agency's methods and skills. By 1948, the House Un-American Activities Committee hearings about communist influence on the country were underway, and the FBI wanted a movie about this hot new topic, but Small refused to grant the FBI power to approve the screenplay, so Hoover insisted all traces of the agency be removed from the film. Small refused, holding that fictional treatment of a public agency was legitimate. The only concession Small made was regarding the title, consequently The New York Times published a letter from Hoover disavowing any connection to the film and stating that he had not sanctioned it.

The New York Times film critic, Bosley Crowther wrote well of the screenplay, "No use to speak of the action or the acting. It's strictly routine. But the plot is deliberately sensational."