On a planet whose human inhabitants have barely become more interesting than other species of ape, a black obelisk appears. It ensnares the mind of any human who comes near and sets them a task. The tasks vary in complexity and duration, but the results of success and failure are always the same: for failure, stabbing pain and an explanation of how to do better, for success, ineffable pleasure and delicious food and a harder task. The humans strive to please their alien god, accomplishing successively greater feats of dexterity and intelligence and clearly becoming a nascent civilization. Of the three viewpoint characters, one fails too often and loses the obelisk's attention entirely; the other two excel with fire and stone tools and twisting string and drawing primitive maps. The descriptions of their devotion to the obelisk and the experience of communing with it are blatantly and unashamedly horny, but none of the sexiness involves body parts in any way. Eventually one of the protagonists invents the first alphabet, and is rewarded with a vision of their descendants walking on the planet's moon, where a second obelisk awaits them. The novella ends shortly thereafter with the two successful protagonists being told to produce offspring with each other.

On a planet whose human inhabitants have barely become more interesting than other species of ape, a black obelisk appears. It ensnares the mind of any human who comes near and sets them a task. The tasks vary in complexity and duration, but the results of success and failure are always the same: for failure, stabbing pain and an explanation of how to do better, for success, ineffable pleasure and delicious food and a harder task. The humans strive to please their alien god, accomplishing successively greater feats of dexterity and intelligence and clearly becoming a nascent civilization. Of the three viewpoint characters, one fails too often and loses the obelisk's attention entirely; the other two excel with fire and stone tools and twisting string and drawing primitive maps. The descriptions of their devotion to the obelisk and the experience of communing with it are blatantly and unashamedly horny, but none of the sexiness involves body parts in any way. Eventually one of the protagonists invents the first alphabet, and is rewarded with a vision of their descendants walking on the planet's moon, where a second obelisk awaits them. The novella ends shortly thereafter with the two successful protagonists being told to produce offspring with each other.