Ray Milland performs admirably in this suspenseful story set against a backdrop of Cold War tensions. He portrays "Fields," a scientist who is supplying photographs of confidential information to individuals abroad for payment. The question arises: is he acting on his own accord, or is coercion at play? What follows is roughly ninety minutes depicting considerable inner turmoil as he transmits more and more data to the mysterious "Mr. Bleek" (Martin Gabel), all while growing increasingly repulsed by his actions. He turns to alcohol for solace, but that won't alleviate his situation when one of his messengers dies unexpectedly and the FBI uncovers proof of spying. His apprehension is justified as they begin compiling a roster of potential spies—and he anticipates being included on it. Contributing significantly to the drama’s intensity is the absence of spoken words; Herschel Burke Gilbert’s musical score carries the emotional weight, and it succeeds admirably. It fosters feelings of anxiety, irritation, dread, and alarm, while Milland, along with the recurring sound of a telephone ringing, conveys a distinct feeling of desperation as events progress. I can't say that the ending resonated with me, but its straightforwardness, the tightness of the direction, and the ambiguity surrounding who is responsible all combine to make for a fairly captivating experience.

Source on TMDB