What happens
Jerry and Joan climb a concrete shaft inside the Euclidean island while Captain Bradford and Mrs. Gregory wait aboard the Gregory yacht, which must leave the lock by eight o'clock. The young pair sabotage the island's machinery, then reach the sound chamber and the private elevator leading to the control room on the surface. Joan intends to subdue the guard with her ray gun so Jerry can send a radio message to Johnson. Their barefoot, exhausted progress is tense as the island prepares to submerge, and their message gets through. The yacht is taken back into the lock, and the island begins to go under.
The Euclidean island, a magic island that submerges, including its concrete climbing shaft, sound chamber, control room, and the Gregory yacht waiting outside the lock.
Characters: Jerry Hall, Joan Gregory, Captain Bradford, Mrs. Gregory, Johnson, Klyastra
Listen for: Jerry and Joan's climb up the concrete shaft, their radio message to Johnson, and the alarm signals announcing the island's submersion.
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.