The Quest team is looking for trinoxite, a new metal vital to the space program. They're in the field (probably Peru), checking out a very pure specimen obtained from an Indian, when a canoe drifts by. Inside is the Indian! He tells how a giagantic turu--a bird--snatched his brother and flew off.
Investigating the team learns the "bird" is actually a giant pteranodon--a bird like dinosaur thought extinct! And it obeys a strange old man who lives on a plateau! The old man is forcing natives kidnapped by Turu to mine trinoxite, which he thinks is valuable silver. He commands Turu to kill Dr. Quest and Race, but Race wins that fight, thanks to a trusty bazooka. Stunned, Turu falls from the sky into the tarpits. Desperate to save his only "friend", the old man follows him in.