 When three employees of a bank are found murdered with cobra venom, Charlie Chan connects the homicides to a case that he had worked on in Shanghai in 1937. Even though he arrested the alleged murderer, 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 and he later escaped from the police. Although Chan believes that he is involved with a gang that is stealing valuable radium from the 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 is on the right track.