This is a slow-paced but solid film about a police inspector, played by the calm and unruffled Eric Portman (the spider) and his quarry, a master thief and safe cracker (the fly), who is played by Guy Rolfe. Rolfe was excellent in another film which he made this same year, PORTRAIT FROM LIFE (1949, see my review). He is just as good in this one as well, though playing a very different type of character, and one far less sympathetic. Robert Hamer directed this, one of only 14 films which he directed. He retired from the screen at age 49 and died at age 52, hence the small number of his films. He is best remembered for directing KIND HEARTS AND CORONETS (1949), this very same year, with Alec Guinness. The love interest in this story is played by the Romanian actress Nadia Gray, who has both men in her thrall but has a wild passion for Rolfe which at first he does not return. This was only her second film, the first being a French film in this same year which has never been reviewed on IMDb and may be lost, or at least lost to memory. Portman finally catches the elusive Rolfe and send him to prison, but then a wartime situation arises which requires a crucial document to be stolen from the safe of The German Legation in Switzerland. Portman recruits Rolfe for this task and the thief thus uses his safe-cracking and building-climbing skills to get the document and fight the Germans. It is a good film, well made, but somewhat slow. It would not have seemed so in 1949, perhaps, but things have speeded up now.