Book 6: from the depths of time, part one

After a visit to the distant future, the crew of Valentinian discover that the galaxy has been overrun by Centaurs. After failing in an attempt to prevent the invasion at its point of origin, the planet Copernicus, their only option is to contact Temporal Security. But despite their efforts, the Centaur invasion soon reaches Earth, and Temporal Security is powerless to stop it. The invasion is somehow connected to a xenoarchaeology expedition that was murdered on an alien world, but who somehow all returned to Earth safely. When time is fractured by the Centaurs to enable them to invade numerous points in history at once, the crew of Valentinian find themselves scattered across time.