In the episode titled Aboard a Test Rocket Plane, the Gregory party finds themselves trapped in the underwater city of Euclidia, where hope seems to dwindle. After hearing a radio broadcast from Los Angeles announcing their deaths, their situation appears increasingly dire. The Euclideans, who have captured them, initiate an artificial volcanic eruption, further complicating any potential rescue efforts. While Mrs. Gregory and Joan remain in their quarters, Captain Bradford and Jerry are granted access to the rocket ship laboratories, where they hope to uncover vital information about the Euclidean technology.