- Director:Sobey Martin
- Writer:Irwin Allen,Bob Mitchell
- Cast:Gary Conway,Don Matheson,Stefan Arngrim
|Episode cast overview:|
|Gary Conway||-||Capt. Steve Burton|
|Don Matheson||-||Mark Wilson|
|Stefan Arngrim||-||Barry Lockridge|
|Don Marshall||-||Dan Erickson|
|Deanna Lund||-||Valerie Scott|
|Heather Young||-||Betty Hamilton|
|Kurt Kasznar||-||Alexander B. Fitzhugh|
|Whit Bissell||-||Dr. Krane|
|Joseph Ruskin||-||General Aza|
The set for the City of Limbo was a redress of the underground mutant city constructed for the motion picture Beneath the Planet of the Apes (1970).
In another connection with the Planet of the Apes movie series, pay close attention to the steps within the secret city. They are the Mutant's set from Beneath the Planet of the Apes (complete with the small Arena Taylor and Brent fight in). They have been painted blue and are shot from behind, but several sets show clearly the melted spots on the bannister's and the area where the mutants stand while interrogating the captive Brent.