the hardy boys hear a mysterious call for help on their shortwave radio set: "help -- hudson". meanwhile, fenton hardy is investigating nation-wide thefts of radio equipment by a group of criminals called "the hudson gang". but of more immediate concern is the theft of several auction items, at an auction attended by chet morton and the hardy boys. the stolen items are mostly animal skins and carcasses intended for use in taxidermy, chet's latest hobby.