A U.S. Navy expedition, led by Commander Hal Roberts, embarks on a mission to Antarctica to investigate mysterious reports from an earlier probe. The team, including reporter Maggie Hathaway and Lieutenant Jack Carmen, faces severe weather and erratic equipment behavior, ultimately forcing their helicopter to crash land in an uncharted tropical valley hidden deep within the icy continent. This enigmatic place teems with prehistoric flora and fauna, an ecosystem cut off from the rest of the world for millions of years. As they strive to repair their damaged helicopter, they grapple with the dangers posed by the strange and hostile environment.

While exploring the valley, the group encounters an array of ancient creatures, from ferocious dinosaurs to enormous plant life, which test their survival skills. They also come upon a reclusive figure who has somehow survived in this lost world, adding further complexity to their predicament. With limited resources and time running out, the team must navigate not only the physical threats but also the psychological strain of their isolation. Their hope hinges on ingenuity, resilience, and the slim possibility of rescue as they work against all odds to find a way back to civilization.