In the near future, an immense hollowed-out asteroid has appeared in the solar system, slotting neatly into Earth orbit. The Stone, as it's called by the American explorers, has six habitable chambers in a classic O'Neill configuration, and two alarming mysteries. First, the seventh chamber is larger than the length the asteroid, stretching down an artificial linear singularity to unimaginable distances. Second, the Stone's derelict cities contain libraries with books published centuries ahead, and those histories say that in a few weeks, NATO and the USSR will start a nuclear war that kills billions. Can the explorers of the Stone figure out its mysteries in time to change history?

Bear's answer is a resounding "No". The bombs go off, billions die, and our heroes are unable to change fate. There's a great deal of realism as seen through the eyes of our primary heroes, mathematician Patricia Vasquez, the engineer and manager Lanier, and Soviet soldier Mirsky. But as the bombs fall, Deus descends from his machina: The post-human inhabitants of the Stone have moved millions of kilometers down the seventh chamber to Axis city, where they are divided into political camps matching a philosophical split going back to the millennial past (in their timeline) nuclear war, and a present plan to end their own war with the alien Jarts through turning their city into a super-weapon.

There's a lot of cool stuff, and some great retro Cold War paranoia. But I'm not sure the big ideas about the nature of the infinite tubular universe really click. And while I'm not yet in the camp of "Greg Bear can't write women", which some people reviewing Legacy said, the few sex scenes felt obligatory and weirdly fetishistic.