Four humans find themselves in "The System", 4 Earth-like planets linked by gates. There are four sentient peoples, human-like, but with some confounding differences. The humans earn kahlia, a neural enhancer that merges with your skull. The kahlia bestow a sixth sense, leova, the ability to sense the emotions of those nearby. When the humans discover the kahlia allow them to feel others nearby having sex, they are forced to re-evaluate their feelings for each other, the system's peoples and their sexuality. And there is "the task", the real reason they are in the system. Learning what the task is proves difficult, completing it changes the lives of the system peoples forever. Like all good mysteries, there is a sting in the tail, revealed long after the humans return to the Milky Way.