In Book II of the Critical Mass Saga, Thorsson Krey, a remnant warrior from the anarchic underground of Earth's late 21st century, along with Sky, a kindred spirit from high in the ranks of the now abandoned Fleet of human survivors left behind during their attempted genocide, along with one of the elder M'ahk Tehrill, themselves, flee to protect Ar'Jvikkah, the offspring of the alien Queen and custodian of all that is left of a collective history passed down by this dignified ancient race of travelers who Thor discovers are connected in a very deep and historic way to the human race, as they begin their own exodus, full circle, back toward what they believe will be a healed planet Earth.... PLANESHIFTERS continues this exodus as Krey and the tattered survivors of the Algol supernova, along with the few who remain dissident at their side, flee a tachyon shockwave originating from the birth of a new black hole created from the massive cataclysm. Harnessing the unimaginable power threatening to sweep them from behind, and reaching impossible speeds as they begin to shift in and out of space and time, they near one of the Fleet's botched terraforming planets, Cheops: a hostile rogue planet near the blue giant Alcyone, and they stop to assess their situation, only to find that things have been forever altered.... As the mystery of their newborn connectivity with space and time unveils, so does the presence of a hostile and relentless terror, sent from their own past, seeking to shut them down before they can learn its long-kept secrets and harness this power as a key to the free travel of the known planes of existence, or as a universal weapon of unimaginable power.