Cluster is book one in the Cluster series. The story centers on Flint, a stone age barbarian from the planet Outworld, of the Sphere Sol. In the far future, the milky way galaxy is home to several species, each with it's own Empire. These Empires are centered on the species' home star, and extends hundreds of light years in every direction, forming an imaginary sphere (ball) encompassing many star systems. These systems decrease in development as distance from the center increases, e.g. Capella, 45 light years from Earth is in a renaissance period, while Flint's planet of Outworld (over 100 light years) is literally in the stone age. Sphere Sol is centered around Earth with its sun, Sol.

The technology of the day includes instantaneous matter transmission (mattermission) to any part of the Galaxy, but the expense is prohibitive. Only small message capsules are usually sent. To send a person costs trillions of dollars. What is needed is Identity-Pattern Transfer, the technique of transmitting the essence, the aura or soul, of an individual into another body, called a host. This aura is known as the Kirlian Aura, and is different in all living beings. Some have normal, maybe 1 or 2 points, while others have very high Kirlian, maybe up to 100 or more.

One day, an envoy from a technologically advanced sphere Transfers to Earth and offers to freely give the Sphere Sol Council the secret of Transfer. The Sol Ministers are naturally suspicious as this technology would be worth untold wealth. It turns out that the alien is not acting out of the goodness of it's heart. The Milky Way Galaxy is under threat from the Galaxy Andromeda, who wish to solve their own energy crisis by 'stealing' the fundamental atomic energy of our Galaxy, leaving us, quite literally, in the dark. To accomplish this, Andromeda must build Power Transfer stations all over the Milky Way. Discovering and destroying these stations is paramount.

The alien is part of a pan-galactic coalition, which aims to defeat Andromeda simply by means of vigilance. Sol, in return for the secret of Transfer, is to contact every sphere within 2000 light years, give them the secret of Transfer, and bring them into the coalition. Those spheres must then branch out further until everyone is participating against the threat.

The Sphere Sol Council must find the people with the highest Kirlian Aura for this Transfer work. Because once Transferred, the Kirlian number represents how long that person can be in the host body before his/her essence is 'absorbed' into the host. At that point he/she would cease to be what they were and become what the host was.

Flint of Outworld is chosen to go Galaxy hopping and contact alien spheres because he has the highest recorded Kirlian Aura in the galaxy ... 200 times higher than normal. Even though he is a huge cave man with green skin, and runs around naked hunting dinosaurs ... and has no concept of reading or writing, the next highest Kirlian Entity in Sphere Sol is Female, and only rates 90 on the Kirlian Scale. A strong life force is necessary for Transfer because it quickly begins to fade—the stronger your 'spirit', the longer you can stay in an Alien body in an unknown civilization billions of miles from home.

So the jolly green giant is sent backpacking around the Galaxy, making contact with other species in more ways than one. The Galaxy Andromeda, understandably, is not too happy with this turn of events and sends its own high Kirlian agent to deal with Flint. It turns out that you cannot switch sex via Transfer, so a number of interesting liaisons occur. Interesting, that is, because they are both in alien bodies—and most of the alien species have vastly different ideas and mechanisms of reproduction. Witness the tri-sexual Spicans in chapter five. Piers even provides diagrams :-)

Overall, this is a very enjoyable book. It doesn't get bogged down in techno-babble, and has interesting and credible characters—in short it's the perfect opener to a series. The aliens don't need to conform to scientifically deduced conceptions—the story itself isn't really a space opera at all, but rather an original work of fiction that asks the age-old question—is there a right side in any conflict? Andromeda can justify its pursuit of energy, and the Milky Way can justify its violent defense. Both sides are right and wrong, so who should the reader be rooting for? Don't ask me, buy the book and read it for yourself.