The Skinner tells the story of three individuals who have journeyed to the 'line-world' (a world on the 'line', or border, of the Human Polity) of Spatterjay, a hostile mostly aquatic world with ferocious native lifeforms.
The planet Spatterjay is host to a complex virus that permeates throughout all life forms (including humans), propagated by a kind of leech which uses the virus to keep its prey alive whilst it feeds upon them.