Synopsis: From the front flap of the Tor first edition: "...Now in the sequel, Probability Sun, Kress returns to the future in which the human race is losing an interstellar war against the mysterious alien Fallers. A shipload of scientists from Earth is sent to study the enigmatic artifact discovered on a distant planet, while the military crew of their ship is secretly holding prisoner for study, the only live Faller ever captured. The artifact is not only a powerful weapon, but possibly the key to a lost superscience that the Fallers may have decoded. Or it may be a doomsday machine for everyone, human and alien."