A marine biologist and a government agent investigate mysterious deaths and rumors of a sea monster in a secluded ocean cove, and find themselves involved with a marine biology professor conducting secretive experiments, international spies trying to steal his secrets, a radioactive light on the sea bottom, and the malevolent thing which guards it.

This Warner Bros. The Sports Parade series short chronicles the attempt by a group of men to navigate the Colorado River through the Grand Canyon to Lake Mead. Led by Norman D. Nevills, nine men undertake a nineteen days trip in three specially built rowboats through the more than 200 rapids, some which run at 30 mph. Along the way, they see the remnants of previous expeditions. They also visit abandoned Pueblo Indian cave dwellings.