Parasite is a novel written by Richard Lewis. It was first published in 1980.
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Chaos ... insanity ... death
When Peter Braddock planned the perfect crime, he never imagined the horror he was about to unleash on Britain. The circumstances were bizarre - the abandoned cruiser he had spotted in the English Channel .... the fearfully mutilated body in one of the cabins ... the blood. But how could he ever guess what happened when he boarded it?
The stricken boat held a gruesome secret. Clinging to it and travelling with it were the tiny carriers of a fearsome disease ....