Five years ago, PEN/Faulkner Award-winner Sabina Murray published a story collection about global explorers from various eras, including Balboa, Magellan and William Dampier. “Tales of the New World” offered an all-male lineup — except in its opening novella, “Fish,” about Mary Kingsley who, in the late 19th century, ventured into the interior of Africa, collecting specimens to turn over to scientists back in England. “Fish” took a feisty look at a maverick who pursued her own path through life and delighted in others who did the same. Among them: Roger Casement, defender of indigenous rights in the Congo and the Amazon, covert homosexual and eventual martyr to the cause of Irish independence.

(Grove)

Now Murray has returned to Casement in a novel that spans 30 years, starting in 1886, as it takes on questions of friendship, love, conscience and conflicted identity. It’s a big, ambitious book guided by the same intelligence and sly prose that distinguished her portrait of Kingsley. If “Fish” was the launchpad for Murray’s exploration of globe-hopping eccentrics, “Valiant Gentlemen” is the glorious voyage.

The narrative circles around a romantic triangle in which three people handle one another with an unpredictable mix of generosity, tact and blindness. A friendship between Casement and artist Herbert Ward serves as the backbone of the book, while Ward’s wife, Sarita, an Argentinian American heiress, provides all sorts of unexpected tonic notes.

The two men meet in their early 20s while working in the Belgian Congo, opening up trade routes to bring out ivory and rubber. They enjoy a close, playful rapport, while sharing misgivings about their employers’ brutal treatment of the native workforce. They’re also compromised by the company they keep — especially Ward, whose drunken purchase of a kidnapped tribeswoman (“He had thought it valiant at the time”) — threatens to mire him in a scandal involving cannibalism, slavery and torture.

Casement’s quandary is more subtle. Growing aware that his “love for his friend” may be “something else,” he turns to casual gay trysts to slake his desires. In Victorian England, that’s a crime, and he has to conduct himself discreetly for the sake of the overall good he’s trying to do.

Murray spices things up with cameo appearances by Kingsley, Belgium’s King Leopold and novelist Joseph Conrad (making the Congo River journey that will inform “Heart of Darkness”). But it’s Sarita who repeatedly helps the novel achieve liftoff. Her appraisal of Casement’s feelings for her husband is more sympathetic and sharp than Ward’s. As she raises five children, she encourages Casement to feel welcome as their honorary uncle.

Murray, in her acknowledgments, says she was inspired by her fascination “with what it was like to be these people unaware of what the future held.” That future is leading, of course, to World War I, which will find two of the Wards’ sons on the battlefield, while Casement angles for German support of Irish independence in ways that mark him as a traitor to England.

Author Sabina Murray. (Kathleen Hennessey)

Murray is canny in tracing the near-imperceptible stages by which Casement and Ward land on opposite sides of bitterly divisive issues. As the novel progresses, Murray’s scrutiny of Casement’s dilemmas of identity grows evermore shrewd. If Ward has little reason to question the furnishings of his life, Casement’s split loyalties make his existence feel increasingly untenable. From the start, he sees himself as someone “who is Irish when he’s not being British, British when he’s not being Irish.” This stems partly from pure pragmatism. “Most ambitious Irishmen end up in England, or working with the English,” he explains to Ward. “It’s an economic necessity.”

Casement’s homosexuality throws a wild card into these calculations. He knows enough to keep it under wraps, because exposure would damage both the causes he embraces and the friendship he treasures. Glimmers of war on the horizon — sometimes laughed off, sometimes inducing anxious disbelief — create another source of tension for all involved.

Murray’s parsing of these escalating risks is superb. She has a knack for alluding to the era’s public events and concerns in a manner that lets us understand their impact and influence without her laboring over their details — an indispensable gift for a historical novelist. Her present-tense prose is alternately epigrammatic and elliptical, and her dialogue sometimes Wilde-worthy.

The best thing “Valiant Gentlemen” does — so subtly that you aren’t always aware of it — is trace the erosive process by which its characters transform from young, seemingly immortal crusaders to battered, doubt-plagued figures, compromised in both health and spirit.

“Compassion is not mightier than the sword,” a discouraged Casement reflects at the book’s midway point. “Compassion is an indulgence, or a condition — somehow profoundly powerful in its experience yet diminishing to naught in its deployment.”

The key question the book asks — and Sarita, as spectator to the strains on her husband’s and Casement’s friendship, naturally, is the one who asks it — is this: “What draws people to people?”

That query, so simple, yet rife with complications, informs every fine strand of this wise, illuminating novel.

Michael Upchurch is a novelist and a former Seattle Times book critic.

Valiant Gentlemen

By Sabina Murray

Grove/Atlantic. 489 pp. $27