What happens
Jerry Hall, Captain Bradford, Joan Gregory and Mrs. Gregory descend into the island of Euclidea and are separated one by one in its underground corridors. Each is seized and questioned in the dark by a stern interrogator, first Hall, then Bradford and Joan, who all want to know where the others are. The group eventually reunites and is confronted by G-47, who demands the secret formula Captain Bradford carries. Refusing to give it up, the travelers learn that the island is being submerged beneath the ocean, with warships waiting above. The story is part of the Magic Island series.
The underground city of Euclidea, beneath the island and roughly 200 feet below the ocean surface
Characters: Jerry Hall, Captain Bradford, Joan Gregory, Mrs. Gregory, Tex, G-47, Cleostra
Listen for: The voice of G-47 and the interrogation scenes in the dark
Written from the episode itself; it never gives away the ending. Every recording is remastered for the stream: cleaned of rumble, hiss and mains hum (and the old TV whine where we found it), then levelled in two passes to steady broadcast loudness, so one show is never quieter than the next.