human space and takes Truesdale to a Human outpost colony called Home in an effort to divert attention away from Earth. During their journey they battle with scout ships from the Pak fleet. Brennan and Truesdale arrive at Home only to have Truesdale realize that Brennan plans to convert the colony into a defensive Human Protector army. Truesdale kills Brennan and lands on Home, but is himself infected with a mutated strain of the Tree-of-Life virus that quickly spreads to a number of other colonists, thus carrying out Brennan's plan despite Truesdale's initial attempts to thwart it. Upon his conversion to Protector form, Truesdale immediately comes to view Brennan's plan as necessary and completes it by breaking out of hospital confinement and infecting the entire population of Home. The modified virus either kills or converts the remaining inhabitants, resulting in an army of childless Protectors. The new Protectors think that they absolutely must act quickly to save the rest of Humanity, and start preparing for battle with the Pak invasion fleet. As an aside, it is mentioned that during his sojourn in the outer Solar System Brennan had engineered a genocide on Mars, sending a large ice asteroid to crash into the planet in order to raise the water content of its atmosphere. Water is lethal to the Martians' metabolism, thus this effectively wiped out the species. This incident serves to underscore the Pak Protectors' inherent xenophobia and utter ruthlessness in pursuing their ultimate goal of protecting their descendants. The events which impelled Brennan to this action are those narrated in "How the Heroes Die" and "At the Bottom of a Hole", two short 1966 stories which Niven originally published in Galaxy Science Fiction and later collected in Inconstant Moon. As depicted in these stories, there were two incidents in which Martians killed some humans who landed on their world, after which humans just left Mars alone. In the mind of the Protector Brennan – committed to defending humans and having no consideration whatever for others – that was sufficient reason to exterminate the entire species. Concepts Pak A species called Pak lives on a planet near the Milky Way core. The species has three main stages of development: Child, Breeder, Protector. A Pak is born, and matures into a Breeder, at which point he or she may bear children. Breeders are not particularly intelligent. Around 40 years of age,