One night, upon returning to the cave that his tribe calls home, the monkey-humanoid Moon-Watcher finds a strange crystal object, a kind of monolith that fascinates him at first, but then quickly loses his interest when he discovers that it is not edible. Soon after, the true purpose of the monolith is revealed to be none other than penetrating the minds of our ancestors to induce new abilities that, over time, will cause the development of an intelligence capable of creating new technology.