Though the basic plot for this was extracted from Edgar Wallace's novel Angel of Terror, the cold, cynical characters are very much of the 1960s. They are more memorable though than the bland, insipid individuals who tended to be a more usual feature of this Merton Park series. There are so many potential snags to Richard Leech's initial blackmail and murder scheme, as to strain credibility, but the fast-moving storyline and devious characters prove gripping. In addition to Maxine Audley as Leech's frosty wife, there's Patrick Magee, at home as a menacing police official and Dudley Foster who was always a treat as smooth, sly operators from both sides of the law. Another plus is the superb, sharp photography from Jimmy Wilson, an unsung hero of British 'B's making good use of the ice-rink setting and the exterior scenes, filmed during the 'big freeze' of 1962-63 when snow lay on the ground for several months.