The Optimists by Andrew Miller

Clem Glass, a photojournalist, returns from Africa to London convinced there is no hope for mankind.

Yet after his sister falls ill and he takes her back to the West Country of their childhood, he cannot ignore the decency and kindness he encounters, or the pulse of goodness in his own heart. When news comes offering Clem the chance to confront the author of his nightmares, he must choose what sort of man to be.