What happens
Jerry and Joan sneak through the lower levels of the Euclidean island while the Gregory boat prepares to escape at eight o'clock. Captain Bradford and Mrs. Gregory wait aboard the boat, anxious over the children's silence and the gong that sounds the alarm level by level. Joan and Jerry sabotage machinery, flood a section of the island, and race past pursuing guards toward a steep shaft that leads back up to the surface. Their route is dangerous, and it is unclear whether they will reach the boat in time or whether the island will be submerged. The episode ends before the escape is resolved.
The Magic Island of Euclidea in the South Seas, and the Gregory yacht waiting nearby.
Characters: Jerry, Joan, Captain Bradford, Mrs. Gregory, Pat, Tex, Mac, Nick
Listen for: The gong strokes that mark each alarm level, and whether Jerry and Joan can climb the shaft before the island is submerged.
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.