Gerleesh has watched her home world destroyed, killing everyone she ever loved or knew. Last of her people, old and weary and all alone, she just wants to find a home where she can live out the rest of her life in peace. She comes to ancient Earth, and encounters primitive humans. She is amazed to learn that she might actually find friendship there, just as disaster strikes.

Little Bear of the Long Spear tribe faces the ugliest monster he has ever heard of. Instead of killing it, he begins to make friends with it—just before it is killed, and Little Bear is struck down along with it.

When he wakes, he finds that all the world is different, and he has changed most of all. But that may not matter, as temperatures plummet and all living things are threatened by a descending ice age. Only the most adaptable have a chance to survive.