Sherlock Holmes (Arthur Wontner) and Dr. Watson (Ian Hunter) are determined to protect Mary Morstan (Isla Bevan), a frightened young woman who is threatened by an escaped murderer. The killer is looking for a stolen fortune, and revenge on the man who stole it. Now he's at Mary's door and Holmes and Watson must look for answers in a freakish carnival filled with pygmies and tattooed men. When Mary is kidnapped, it becomes a desperate race against time.