During the time of cavemen, there existed an already-ancient race called the Reiign who had an extensive empire. They were strong and powerful for many millennia, explaining and encouraging others to utilize their philosophy of peacefully getting along with one's neighbors, whether next door or in outer space. They also taught many species about their advanced technology from their portion of the Milky Way. Unfortunately, their movement toward all-encompassing self-determination is halted by invading marauders from the Magellanic Cloud. The clash of equally ancient but completely opposite cultures leave the Reiign, a race for thousands of years unable to show any signs of aggression because they underwent a process of genetic cleansing, at a distinct disadvantage.
When one is desperate enough, one will try anything to solve a problem. So a band of scientist escaped and went to the last safe place in the galaxy. Knowing that they had only one chance left, they developed a plan that they hoped would defeat the bad guys. Their plan, which has been in the works for fifty thousand years, culminates in the creation of the perfect warrior. He is bred for aggression and optimized for war - and conditioned to not flinch from the shedding of blood of many. They invented the ultimate killing machine: man.
This is a very imaginative book, while at the same time not being so far-fetched that it becomes unbelievable. Lewis does an excellent job of inventing otherworldly creatures - and makes a good case for other beings having "invented" humans to do their killing for them. The plot is good, though it drags in a few places. The characters are so convincing that you can almost see them.