The famous explorer-scientist, Doctor Manners, prepares to embark on an expedition to South America, to prove that the continents were once all connected. Manners is traveling with his niece, Gail, police forensics scientist, Barry Allen, Picture News reporter, Iris West, and her nephew, Wally. With Manners, Gail, and West waiting at the dock, Allen takes Wally aside, and reveals his secret identity, as the Flash. Allen and West, as the Flash and Kid Flash, race to the waterfront. The Scarlet Speedsters take time out to clear the streets of all civilians, as a troubled plane comes in for a landing. Once aboard the boat, and well on their way, Manners lays out his theories as to why he believes the continents were all, once, a single land mass.
Manners hopes to find either an aardvark, or a lemur, in South America, proving that it was once connected to Africa. Upon arrival, the expedition party finds that their native guides refuse to lead them through the "Valley Of The Sleeping Giant". The "Sleeping Giant" is really a volcano, which, shortly, erupts. The volcano's eruption touches off a violent ground tremor, which hurls the expedition party down the mountainside. After setting up base camp, Allen and West seek out the high ground to get an overview of the surrounding area. There they discover an enormous human footprint. Allen and West offer to do some scouting. Unbeknownst to the rest of the party, they will do so as the Flash and Kid Flash.
Responding to a cry of distress, the Flash and Kid Flash discover a primitive, being menaced by a gargantuan avian horror. The Scarlet Speedsters drive the feathered monstrosity away, then follow the primitive to his village. The primitives keep saying the word "Grodan", but their language is unintelligible to the Scarlet Speedsters. The Flash and Kid Flash are brought before the tribe's historian. Judging by his paintings, the Flash determines that "Grodan" means "Giant". As if on cue, an enormous golden hand grabs the Flash. Vibrating at super-human speed, the Flash is able to send a shock down the giant's arm, before the giant can crush him to death. The Scarlet Speedsters lead the giant away from the tribal village, then collect some cable from their own base camp.
After using the cable to trip the giant, the Scarlet Speedsters bind him. At the giant's defeat, an eclipse begins. With no eclipse scheduled for any part of the world, the Flash's suspicions about their surrounding are confirmed. Somehow, the ground vibrations, triggered by the volcano's eruption, has sent them back, millions of years into the past. The Scarlet Speedsters race around the globe, confirming both the Flash's fears, and Manners' theory regarding a super-continent. Suddenly, the sea begins to flow into the crack, between what will become South America and Africa. The oceanic force begins to divide the land masses. The Scarlet Speedsters evacuate the tribal village. A horde of Giants charge the Scarlet Speedsters.
Before they can reach them, though, the Giants are swept away by the rapidly rising sea. The Scarlet Speedsters race back to the base camp. Moving so fast as to be naked to the human eye, the Flash takes ahold of Manners and West, while Kid Flash grabs Gail. Matching their vibrations to the exact frequency of the volcanic ground tremor, the Scarlet Speedsters proper everyone back to the present. The Flash and Kid Flash, as Allen and West, rendezvous back with the expedition party. Though the base camp has been destroyed, Manners was able to preserve his camera. His photographs of lemurs, in South America, clearly prove that the continent was once connected to Africa. Allen chooses to remain silent, regarding their trip through time.