Every living thing has a Kirlian aura that can be measured. Through transfer, the mind and personality of individuals with high aura can be sent to animate a body physically distant. For instance, a transferee living on Earth could be sent to Outworld and inhabit the body of one of that planet's stone-age tribesmen. Transfer is a refinement of mattermission technology, but because only the aura is transferred, it is substantially less expensive. In the first three novels, the protagonists find themselves transferring from alien body to alien body in order to combat threats from elsewhere in space. Thousandstar and Viscous Circle These later novels take place between Chaining the Lady and Kirlian Quest. While the original Cluster trilogy tells epic stories of galactic scope, the later two books are smaller stories in the same setting. Instead of transferring to different worlds with each chapter, the protagonists spend almost the full novel on a single planet. See further details below. Relationship with other novels Anthony first conceived of the Cluster series when writing But What of Earth?, a speculative novel in which the government discovers the secret of mattermission, making interstellar colonization feasible. Earth? follows developments on humanity's home planet as its civilization and resources dwindle when half the population leaves for the colony worlds. The Cluster series takes place roughly 500 years further in the future and is in continuity with Anthony's original manuscript of Earth?, published in an annotated edition by Tor Books in 1989. The Cluster series is not necessarily consistent with the first published version of Earth?, the heavily reworked 1976 Laser Books edition credited to Anthony and Robert Coulson as collaborators. According to Anthony this was an unauthorized collaboration. More detail can be found on Anthony's main page. After completing the original Cluster trilogy, Anthony returned to the earlier time frame. His three-volume Tarot series featured Brother Paul of the Holy Order of Vision, a major supporting character in Earth?, and is set some years after that earlier novel. At the same time Anthony wrote the two additional Cluster novels, Thousandstar and Viscous Circle. Series synopsis Cluster (1977) As the story opens, the alien envoy Pnotl of Sphere Knyfh attempts to enlist the cooperation of Sphere Sol in a mutual crisis of galactic proportion: Galaxy Andromeda has discovered the secret of energy transfer and intends to use it to steal the basic energy of the