A scientist working on a plan to protect Allied ships from German torpedoes throws a cocktail party and is mysteriously electrocuted during the gathering of supposed friends. Secret agent Charlie Chan (Sidney Toler) is called in to conduct the investigation, assisted by his daughter, Iris (Marianne Quon), and son, Tommy (Benson Fong). As Chan investigates amid elaborate attempts on his own life, all of the party guests appear to be have dark secrets and motives for murder.