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.