Jon Pertwee and Ingrid Pitt (who plays Galliea) worked together before, in 1971 in an episode of "The House That Dripped Blood". He played an actor playing a vampire, she played an actress portraying a vampire but turns out to be a vampire for real!
This episode takes place in Atlantis in circa 1500 BC.
Ann Michelle was originally cast as Lakis but was replaced due to her unreliability during rehearsals.
This episode was watched by 6 million viewers on its original transmission.