Prendick casts off into the sea… the same place he started his misadventure. Man, not only does this guy have bad luck, but it's circular bad luck.
Anyway, he drifts for a couple of days but is eventually rescued.
He tries to tell the captain and the first mate about his adventures, but they assume the perils he faced on the open sea have fried his brain. Prendick decides not to tell anyone of his time on Moreau's island ever again for fear of being taken to a white room with padded walls...
Terror diseases Prendick's mind. He returns to London, but he sees Beast Folk in the faces of its human citizens.
So, he moves to the downland (southern English countryside). There he lives in relative comfort away from the bustling throngs of London's busy streets. He reads books and performs chemistry experiments, and studies astrology when the night sky is clear.
"There is—though I do not know there is or why there is—a sense of infinite peace and protection in the glittering hosts of heaven. There must be, I think, in the vast and eternal laws of matter, and not in the daily cares and sins and troubles of men, that whatever is more than animal within us must find its solace and its hope. I hope, or I could not live." (22.7)