The title comes from August 25, 1948, known as "Confrontation Day," during which Whittaker Chambers stated:
The story has spread that in testifying against Mr. Hiss I am working out some old grudge, or motives of revenge or hatred. I do not hate Mr. Hiss. We were close friends, but we are caught in a tragedy of history. Mr. Hiss represents the concealed enemy against which we are all fighting, and I am fighting. I have testified against him with remorse and pity, but in a moment of history in which this Nation now stands, so help me God, I could not do otherwise.[4][5]
Senator Joseph McCarthy paraphrased this phrase with his own: "the enemy within."[6]
Goldcrest Films invested £558,000 in the film and received £545,000 causing them a loss of £13,000.[7]