Invisible Sun (Empire Games, #3)

by Charles Stross

The Dome in time line four was an annex of one of these fortresses. The Hive had made several attempts to breach the fortress, but the repeated attacks on time line four were successfully repelled by its defenders. They built a dome atop the invasion gate to monitor and seal it. But despite their local successes, the Hive ultimately prevailed when they changed tactics. They flared the black hole by dropping vast amounts of mass into its accretion disk, then channeled directed bursts of hard radiation through all the gates they’d established. Having killed the defenders and slighted their fortresses, they paused only long enough to ensure that these time lines were unoccupied by hominids—a fimbulwinter caused by dropping a handful of medium-sized meteorites on the planet sufficed—then moved on, leaving behind a minimal watch on the hole that had powered the successful attack on the fastnesses of time. It was a messy fight, and the Hive warriors were less than 100% successful in their clean-up operation.