Two and a half millennia ago, an artifact appeared in a remote corner of space beside a trillion-year-old dying sun from a different universe. It was a perfect black-body sphere, and it did nothing. Then it disappeared. Now it is back. The object - an Outside Context Problem, something the Culture has no framework to understand - triggers a frenzy of activity among the Culture's Minds, who scheme, conspire, and betray each other with an enthusiasm that puts their biological citizens to shame. Meanwhile, the Affront, a deliberately cruel alien species, see the artifact as their chance to rewrite the balance of power. A novel in which the real drama plays out in the communications between starships, and the humans are largely bystanders.