A Victorian professor invents a super-powerful tunnelling machine that can dig its way through the Earth's crust. To impress his financial backer he gives a demonstration, but his invention malfunctions and bores a channel to the very centre of the Earth - where they discover a prehistoric human race enslaved by flying telepathic monsters. Sci-fi adventure based on the book by Edgar Rice Burroughs, with Peter Cushing, Doug McClure, Caroline Munro and Cy Grant.

A huge burrowing machine tunnels out of control at ferocious speed, cutting clean through to the center of the earth, to the twilight world of pellucidar. Once there, Dr. Perry and David Innes are threatened by half human creatures, lizard-like birds, and man-eating plants.