Halo: Silentium

Halo: Silentium is the third and last novel in The Forerunner Saga by Greg Bear and is the sequel to Halo: Primordium. It will be released on January 8, 2013, with an audio edition released simultaneously.

Official summary
"In Halo: Cryptum, Greg Bear began a three-book arc set in the era of the Forerunners, the ancient and enigmatic creators and builders of the Halos, which continued in Halo: Primordium. Now, in the last years of the Forerunner empire, chaos rules. The Flood—a horrifying shape-changing parasite—has arrived in force, aided by unexpected allies. Internal strife within the ecumene has desperately weakened Forerunner defenses.

''Only the Ur-Didact and the Librarian —a husband and wife pushed into desperate conflict—hold the keys to salvation. Facing the consequences of a mythic tragedy, one of them must now commit the greatest atrocity of all time—to prevent an unmatched evil from dominating the entire universe."''

Trivia
"Ur" is a German prefix that means "original" or "primitive".