Complete story — includes the ending
The explorers have a strange guest at the Treehouse who impresses Challenger with his knowledge of geology. Meanwhile something attacks Challenger's electrostatic accumulator. The explorers chase after a group of underground dwellers whom they believe to be the culprits. Their guest turns out to be one of them, and the explorers are soon taken hostage. It turns out that the underground dwellers need Challenger's scientific expertise to help them evolve above ground.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, List of The Lost World episodes. HTML formatting and reference markers removed. · Content license