Dorothy, along with her friends Zeb, the horse Jim, and the kitten Eureka, falls into an underground world after an earthquake. They travel through strange lands like the Glass City, the Vegetable Kingdom, and the Valley of Voices. The Wizard of Oz joins them on their journey, helping them navigate the dangers. They encounter talking plants, invisible bears, and other threats. This part captures a thrilling journey through magical subterranean realms.