Protector (The Tales of Known Space Series)

From the back cover: The Mission of Phssthpok Phssthpok the Pak had been traveling for most of his 32,000 years -- his mission, to save, develop and protect the group of Pak breeders sent out into space some 2 1/2 million years before. Brennan was a Belter, the product of a fiercely independent , somewhat anarchic society living in, on, and around an outer asteroid belt. The Belters were rebels, one and all, and Brennan was a smuggler. The Belt worlds had been tracking the Pak ship for days -- Brennan figured to meet that ship first... He was never seen again -- at least not by those alive at the time.