When three employees of a bank are found murdered with cobra venom, Charlie Chan connects the homicides to a case he had worked in Shanghai in 1937. Even though he arrested the alleged murderer, whom later escaped from the police, Charlie wouldn't be able to recognize him because, at the time of his apprehension, his badly burned face and hands were swathed in bandages. Although Chan believes he is now involved with a gang that is stealing valuable radium from a bank vault, utilizing tunnels that connect to the area sewer system, his new identity remains a mystery. When a detective disguised as a bank guard is found dead in a tunnel by Birmingham, Charlie knows he's on the right track.