LONDON – Jane Austen famously refused to acknowledge the Napoleonic Wars in her books. The detective novelist P.D. James rectifies that in the first chapter of “Death Comes to Pemberley,” her follow-up to “Pride and Prejudice.” She even throws in a corpse.

“Pemberley” is an intensely satisfying mystery that begins six years after Austen’s classic ends. The home of Elizabeth and Mr. Darcy is abuzz with preparations for a ball. So far, so Austen. Then comes the discovery of a dead body in the woods nearby.

As a paid-up member of the Jane Austen Society, the 91-year-old James had long pondered the idea of combining her two great enthusiasms: reading Austen and writing detective fiction. Unsure of whether her creative energy would hold out for a 15th book featuring Commander Adam Dalgliesh, her poetry-writing sleuth, she decided to give this shorter project a try.

“It was fascinating to address what I saw as not defects in the plotting — that would be quite the wrong word to use — but problems, mysteries,” James says over tea in her London home.

Though she has tinkered with some of the details, James channels Austen’s voice with brio. “I wanted to be an echo of hers,” she says.

“Pride and Prejudice” is not James’ favorite Austen novel — that would be “Emma” — yet it was the first she read, finding it on the Sunday school bookshelf when she was 9. She loved it immediately. Years later, sheltering from the Blitz in a London cellar while heavily pregnant with her first child, she reached for it again.

“The noise above was tremendous because of the anti-aircraft guns trying to shoot down these wretched flying bombs, interspersed, of course, with the noise as they landed. It was such comfort reading Austen.” She named her daughter Jane.

A tiny woman in a turquoise cardigan with a silk ruffle, her faced framed by a snowy bob, James sinks back into the sofa, leaning forward when a topic seizes her. As dusk gathers outside, these topics range from Hillary Clinton (she would have been a better bet than Obama, James believes) to the Occupy movement’s London offshoot (she doesn’t have much sympathy for the protesters). She even has views on how much sex the dreary Mr. Collins, who marries Elizabeth Bennet’s best friend, might demand of his wife (lots).

Though animated by exactly the kind of shrewdness you’d imagine a writer of detective fiction to possess, she also radiates an unhesitating warmth.

Yet even in this grand room, with its William Morris upholstery and antique portraits, a darkness dapples her conversation. It’s there when she speaks of her belief in evil and of her ebbing faith in society’s ability to address current economic problems. In the very long term, she believes humankind will go the way of the dinosaurs.

For all that, detective fiction, she says, is an inherently optimistic genre, affirming belief in a rational, comprehensible and manageable universe, and she isn’t quite ready to confirm Dalgliesh’s retirement.