Have you ever seen a mammoth? Kevin Sinclair has!

One night, Kevin wakes up to see a caveman standing outside his bedroom window. When he tells his mother what he saw, she doesn't believe him. She thinks he is acting out his frustrations with his new middle school, making friends, and missing their dog, who has run away. To top it off, everyone at home is anxious because Kevin's dad is deployed on a dangerous mission.

The caveman turns out to be a Clovis boy, a First American, who enlists Kevin's help in retrieving a spear point missing for 13,000 years. Accompanied by his little sister and their teenage babysitter, the trio of time-traveling, 21^st century kids pass through a crack in the Earth at the Murray Springs Clovis Site in Southeast Arizona to find themselves in the Ice Age. Along the way the children dodge prehistoric predators, experience a mammoth hunt, and outwit a mean tribal chieftain to discover that friendship, courage, and honor really don't change over time.