The year is 1828. Brilliant young naval officer Robert Fitzroy is given the captaincy of HMS *Beagle*, surveying the wilds of Tierra del Fuego, aged just twenty-three. But Fitzroy hides a dark secret: hereditary manic depression that can strike at any time. He is seized by two ambitions -- that he can prove, contrary to the spirit of the age, that black and white men are equal; and that he can prove the truth of the Book of Genesis. To this end, he takes a passenger: a young trainee cleric and amateur geologist named Charles Darwin. This is the story of a deep friendship between two men, and the twin obsessions that tore it apart, leading one to triumph and the other to disaster... *This Thing of Darkness* is not just an epic historical novel. By turns gripping, funny, satirical and heartbreaking, it is also a novel about race, religion, science and colonialism that sheds many a light on the state of our world today. It is also one of history's great untold true stories, a tale of men under sail who were prepared to risk their very lives to get at the truth.