The story follows the adventures of adolescent Mark Nye when he is accidentally transported to the Stone Age by his uncle's time machine.

[1] Dr. Robert Nye, a nuclear physicist working at White Sands Missile Range has finally finished his space-time travel machine after 20 years of research.

On the eve of its maiden voyage to Ancient Rome, Dr. Nye's nephew Mark is trapped inside and sent back in time to the year 50,000 BC when a nearby rocket test explosion sends him careening into the controls.

When Mark arrives at his destination he must survive the two weeks it takes the space-time machine to recharge for the return trip with nothing but a few matches, a pocket knife, and a 6-shot .45 revolver.

Mark suspects he is to become dinner, so he shoots one of his guards and escapes, barely managing to evade his captors in an all-night chase.

When Mark and Tlaxcan return to the site of the kill to relieve the guards, they spot circling vultures and suspect an ambush.

This results in a furious chase across the plains, eventually landing Mark and Tlaxcan in a deep cavern where they battle a bear-like creature.

When the tribe learns of what has happened they hold a war council and decide to embark upon a campaign against the Neanderthal settlement.

Boucher and McComas praised the novel for "combin[ing] solid thinking on the elements of time travel with a warmly sympathetic portrait of Cro-Magnon civilization.