When the Princess "Lin Hwa" (Lotus Long) is killed by a poisoned dart in the home of our eponymous San Francisco detective (Boris Karloff) she leaves him one, singly enigmatic, clue which he must utilise to thwart a gang involved with the Japanese occupation of China. Local plod "Capt. Street" (Grant Withers) bucks the trend of many similar style adventure films, and demonstrates some competence as the pair soon discover the foggy docks of their city harbour much more than just ships. There is never any doubt who will come a cropper in the end, but William Nigh gets a lot from his star, a limit...