Is it possible nowadays for otherwise intelligent Americans to reflect on England without thinking first of “Downton Abbey”? To put it another way: Can beleaguered American publishers expect to sell any English author without promising — however absurdly — a tie-in with Julian Fellowes’s opulent confection? I wonder. But in the case of Catherine Bailey’s stylish new book about one of England’s grandest dynasties, the link proves apt.

Readers of “The Secret Rooms” couldn’t ask for a more storied setting or, indeed, for more rooms (a respectable 356). For nearly a thousand years, Belvoir Castle has been the ancestral seat of the Manners family. Bailey, a British television producer and director, initially set out to write about the valiant working men of the Belvoir estate who fought in World War I, a book that surely would have been the more historically valuable contribution. Still, we might forgive her for settling instead on the narrower, intimate family drama contained in these pages.

Here, among other things, is the story of a sad, gentle boy who grew up to be a deeply troubled man. Born in 1886, John Manners, ninth Duke of Rutland, had the misfortune to come of age not only in brutal times but among real brutes. Even by the grim standards of the day, he was the recipient of dreadful parenting. Wasn’t it insult enough to be the “spare” in a world that prized first sons above all others? It could have been worse. Dwindling family coffers aside, a glorious accident of birth assured John an enviably cosseted existence. And the mysterious death of his 9-year-old brother elevated him, at age 8, to the status of heir. So what if Mother and Father thwarted and belittled his every ambition? At least he inherited Belvoir.

But if we know anything from watching “Downton Abbey,” it’s that one man’s castle is another’s gilded cage. John’s was especially claustrophobic. How fitting, then, that he should have spent his final days in some of Belvoir’s smallest, dreariest rooms — the secret rooms of this book’s title. In pages more reminiscent of Edgar Allan Poe than Evelyn Waugh, Bailey opens with John’s death, on April 21, 1940, inside the cheerless Belvoir Castle archives. Exactly what he was doing there — in an oxygen tent, surrounded by several centuries’ worth of family papers, working frantically on something — is the proverbial question.