The Communist Party USA was established in 1919. In 1921 it changed its name to The Workers Party of America. It was banned in 1954 by an act of Congress (the Communist Control Act of 1954). At its peak in 1944 the membership rose to 80.000 members but by mid-1950s it dropped to only 5000 members, including 1500 FBI informants.
Matt Cvetic was a Pittsburgh native requested by the Federal Bureau of Investigation to join the Communist Party of the USA as an informant in the 1940s. By 1948, he earned $85 per week from the FBI for his work, although he continually pressured the Bureau to increase his salary to $100 and threatened to quit if his requests were not granted (they weren't, and he didn't). He told an embellished version of his experiences in a series of articles in the Saturday Evening Post. His experiences were first dramatized in a radio program, which was later adapted for a Warner Brothers motion picture in 1951. He also testified before the House Un-American Activities Committee in the 1950s. Although the radio and film adaptations portrayed Cvetic as one of the party's primary operatives in the USA, he didn't rise above the party's lower echelons. By 1955, Cvetic had been largely discredited as a witness regarding communist activities in the USA because of Justice Department and FBI concerns regarding Cvetic's embellishment of the facts, including an instance in which he claimed to have foiled a Nazi spy plot single-handedly.
At the time of this film, J. Edgar Hoover was in the middle of his 48-year tenure as the FBI's director.
Frank Lovejoy and Paul Picerni, who play brothers, would work again for Gordon Douglas two years later in 'She's Back on Broadway'.
Modern surveillance methods make the equipment shown in this film seem downright archaic. But it was state of the art at the time.