After Samuel Black is killed by a cobra bite, Inspector Harry Davis of the New York City homicide squad telegrams his old friend, Charlie Chan, the famous Chinese-American private detective, for help. Davis knows that Chan had captured Jan Van Horn, an accused murderer, in Shanghai, China, eight years earlier, and the disfigured Van Horn, an escaped felon, was accused of using cobra bites on his victims. Chan, now working as a government agent, arrives in New York and quickly learns that Black and two similar victims were employed by the Sixth National Bank, whose vault holds millions of dollars worth of the government's radium. With the help of his son Tommy and his chauffeur, Birmingham Brown, Chan learns that Ned Stewart, a novice private detective, had been seen with Black on the night of his death. After Stewart tells Chan that he had been hired by an unknown man to watch Paula Webb, the bank president's secretary, Chan checks with Paula, who corroborates his story. Meanwhile, Larkin, a police undercover agent working at Sixth National, disappears after calling Davis for help. Soon thereafter, Davis learns that gangsters Morgan and Taylor were seen in the office of bank president Walter Fletcher, and Tommy and Birmingham follow the hoodlums into a nearby laundry. Discovering a secret passageway from the laundry into the sewers, Tommy and Birmingham uncover Larkin's murdered body. An autopsy concludes that Larkin was also killed by cobra venom, so Chan reasons that there must also be a secret passageway into the bank. Back in the sewers, Chan, Ned and Davis discover a secret entrance into Paula's office. The investigators then go to a nearby coffee shop, whose proprietor, Joe Nelson, tells them that he purchased his video jukebox from Van Horn. Recognizing the jukebox operator's voice from the bank, Chan and Davis search the office of chemical engineer H. R. Jarvis, where they find Lorraine operating the jukebox from a secret room. Chan quickly discovers that Black and the other victims were poisoned by cobra venom when they requested change from the jukebox. Chan then lies to the local newspapers that the government plans to remove its radium the next day, hoping it will force the gangsters to act. While Chan checks the bank's vault, Tommy and Birmingham follow Morgan into the laundry, and become caught in the sewer after the gangsters attempt to blow open the bank's vault. Along with Chan, the two become trapped when their section of the sewer caves in, but Chan uses the telephone lines to send a message in Morse code to David. The police arrive at the bank in time to capture the gangsters and rescue Chan, Tommy and Birmingham. Later, Chan concludes that John Adams, a bank guard, is actually Van Horn, and Paula is his daughter. Van Horn tells how he followed Jarvis to America, believing that he was one of the men who framed him for murder in Shanghai. Chan then recognizes bank officer Bradford Harris as Special Agent Hume of the Shanghai police, and he is arrested as the real killer and leader of the gang. With the case solved, Chan learns that he has been issued a ticket by the New York City police for making an illegal turn.