I've been rereading a novel that I'm increasingly sure is an unacknowledged masterpiece. You may be unaware of it — in the U.S., it's been in and out of print, with more than one title. I've praised it before, but persistence is a virtue and I believe you'll thank me for giving you another chance to discover it.

Harry Thompson's "This Thing of Darkness" was first published in 2005 and, for reasons I can't fathom, failed to make much of an impression. I didn't read it until 2009, when a friend drew it to my attention.

It's a lightly fictionalized account of Robert FitzRoy, who was born into the English aristocracy in 1805, had an extraordinary early career in the Royal Navy, was an accomplished scientist (a pioneer of meteorology), served as governor of New Zealand, and eventually cut his own throat during a spell of acute depression, to which he was prone, in 1865.

All of which would have been excellent material even if FitzRoy hadn't also been captain of the HMS Beagle during its voyage 'round the world with Charles Darwin in the 1830s. The young men's journey to Patagonia, the Galapagos, Tahiti, New Zealand and Australia furnished the insights, one could argue, that created the modern view of the world and man's place in it. FitzRoy's adventures with Darwin and their intense and troubled later relationship form the center of the book.

This astounding proliferation of subject matter could have overwhelmed author and reader alike, but it doesn't. The book succeeds wonderfully on many different levels.

As a straightforward adventure story, it fairly rattles along. Anybody with a taste for historical fiction — especially seafaring tales in the manner of Patrick O'Brian or C.S. Forester — will be instantly drawn in. The period, and the exertions of life aboard a small naval vessel in extreme latitudes, are beautifully rendered.

Thompson enriches that part of the tale with an understanding of what is now called bipolar disorder. FitzRoy was a naval prodigy, the first in the history of the service to pass the tests for officers with a perfect score. He was an intellectual, too — yet revered by his men for his bravery, given to heroic feats, capable of working without rest for days. Then, the thing of darkness would strike, and he'd shut himself away in his cabin for a week, refusing to speak, putting his command and his career in jeopardy.

The 19th century, of course, had no treatment for the condition, and in the end it killed him. One wonders, had it been treated, how much smaller a man would FitzRoy have been?

The book touches on the presumptions of colonialism. Before the voyage with Darwin, FitzRoy commanded the Beagle on an earlier expedition to Patagonia. They encountered Fuegian natives and brought several back to England to be educated — to be civilized — before returning them, as FitzRoy planned, as Christian missionaries. In Britain, they became minor celebrities and were presented at court.

It did not end well, as one would expect. Thompson doesn't disguise FitzRoy's arrogance and recklessness in all this, but he avoids the fallacy of judging him solely by modern standards and describes his motives, and his subsequent dismay, sympathetically. It makes you think.

The more salient theme, though, is the 19th-century contest between science and religion. In this, Darwin represents modernity, and (though he'd trained as a cleric) the evidence before his eyes leads him to shed his faith in established religious teaching without much trouble; FitzRoy, both man of faith and man of science, refuses to yield and is appalled by Darwin's conversion. Again, though, the obvious line of narrative is subverted. In their subsequent quarrels, and in their dealings with contemporaries, FitzRoy is in many ways the warmer and more human of the two. Science isn't everything, and modernity is denied an unqualified victory.

Finally, and most unsettling of all, the book prompts reflection on history and memory. In this telling, Darwin is the minor character in the story of FitzRoy's more remarkable life. So strange: Today FitzRoy is a forgotten man, Darwin a titan of our age.

There'll be no more from Thompson. He died of cancer the year the book was published at the age of 45. He'd been very successful in his other career — as a producer of television comedy — but I hope he'll come to be remembered for "This Thing of Darkness." There's no current print edition in the U.S., but you can read an electronic version, and I urge you to do so.

To contact the author of this article: Clive Crook at [email protected]

To contact the editor responsible for this article: James Gibney at [email protected]