The Black Widow (1947) is a thirteen-chapter Republic serial film.
The Editor of the Daily Clarion newspaper hires writer and amateur criminologist Steve Colt to solve a series of murders, all involving venomous spider bites, with the aid of his best reporter Joyce Chambers.
Meanwhile, the evil King Hitomu has sent his daughter Sombra to the United States to fulfill his plan for global domination by stealing a prototype "Atomic Rocket Engine". Posing as a fortune teller, and assisted by her two loyal henchmen, Sombra sets about stealing the prototype and its secrets by utilizing her cunning nature, array of lethal gadgets, and ability to impersonate any woman she chooses with the aid of masks and wigs.
- Bruce Edwards as Steve Colt, a mystery writer and amateur criminologist working for The Clarion, on the trail of a series of bizarre murders.
- Virginia Lindley as Joyce Winters, a reporter for The Clarion working with Colt, whom Sombra impersonates in order to get close to him.
- Carol Forman as Sombra, daughter and agent of King Hitomu. She is an expert at disguises, manipulation, and planning.
- Anthony Warde as Nick Ward, a small-time gangster hired by Sombra as her personal enforcer.
- Ramsay Ames as Ruth Dayton, a secretary employed by a top scientist on the prototype team. Sombra assumes her identity to steal crucial information on the design and function of the prototype, despite Colt's efforts to prevent her from doing so.
- I. Stanford Jolley as Dr. Z.V Jaffa, a scientist in service to King Hitomu. He assists Sombra by designing her gadgets and creating the masks she uses for flawless disguises.
- Theodore Gottlieb as King Hitomu, the aged and evil ruler of a small foreign kingdom, who dreams of acquiring the means by which he can achieve world domination.
- Forrest Taylor as Bradley, a mob lawyer and acquaintance of Ward's.
- Virginia Carroll as Ann Curry, the only female member of the prototype team. Sombra uses her identity to steal the device and later has her murdered.