Teeny-tiny Hammer pictures built its reputation on second-feature melodramas before graduating to gore-encrusted horror epics. is a low-key thriller starring American actor Robert Preston, whose casting assured a certain degree of business in the States. Preston plays a code expert, resettled in England after the war and working at the British Foreign Office. One morning, Preston's wife is struck down and killed by a car driven by escaping criminals. Preston bypasses the efforts of Scotland Yard and pursues the criminals himself, using his codebreaking skills to track down the "big boys" in charge.