Final installment of Kress's hitherto scintillating trilogy (Probability Sun, 2001, etc.), although by itself this one's barely intelligible. Humanity, exploring through a series of space tunnels, came into contact with the xenophobic Fallers, who thereupon attacked without warning. On planet World, home to furry aliens, xenologists discovered an artifact that, so physicist Tom Capelo found, altered probability; not only that, it could destroy entire solar systems at the press of a button—or protect them. Now, on Earth, Tom's daughter Amanda witnesses the abduction of her father. Why? By whom? She flees to Luna, hoping her friend Marbet Grant might help. Marbet, extraordinarily sensitive to body language, learned how to communicate with the only Faller ever captured. Retired Colonel Lyle Kaufman, a skilled negotiator and now Marbet's partner, wants to go back to World, where his removal of the artifact caused the Worlders' “shared reality” to collapse. The Fallers too have their own artifact. But are they intent on defense or destruction? If both humans and Fallers activate their artifacts on setting Prime 13, spacetime itself may be annihilated. Thus far, the human posture has been defensive. But political upheaval on Earth sweeps the unstable Admiral Pierce into power—and he's anxious to blow the Fallers to dust.
Shapeless, with a somewhat interesting young protagonist, while only minimally renewing our acquaintance with the until-now fascinating Worlders and Fallers: a bitterly disappointing conclusion.