 Detective Philo Vance is called in on a police case in which socialite Montague has mysteriously drowned in a backyard pool at a party held at the mansion of his fiancee Bernice Stamm and her wealthy brother Rudolph. Things take an eerie turn when Vance learns from insane, elderly Mrs. Stamm that the naturally-formed pool was called the  dragon pool  by the original inhabitants of the land and that it harbors a killer dragon.