One of budget-brand Monogram Pictures' entries in the Charlie Chan series, this picture has a busy, tricky screenplay which resembles a serial story. The villain is masked and cloaked in the best cliffhanger tradition, and every few minutes there is some new deadly device introduced (an elevator with a trap door, a weather tunnel with dangerous extremes of heat and cold, etc.). The radio-station setting is novel, and there is some outstanding comedy relief by Mantan Moreland and Ben Carter doing their "incomplete sentence" nightclub act. The direction and photography are routine, but the filmmakers apparently were concentrating on the ambitious technical gimmicks in the script. Par for Monogram, and a pleasant hour for B-movie fans.