When eccentric Victorian scientist Dr Abner Perry (Peter Cushing, Star Wars: Episode IV - A New Hope) and his assistant develop a high powered drill they decide to test its capabilities in a remote Welsh Mountain. The drill proves too powerful and plunges the duo into a vast cavern at the earth's core where evil pre historic birds have enslaved a tribe of humans. Can the Doctor and his assistant help rescue the tribe and escape the evil clutches of their flying nemesis?
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