Louis Bayard, local author of "Roosevelt's Beast" is pictured in his Capitol Hill home. (Sarah L. Voisin/The Washington Post)

Louis Bayard’s daily life is pretty tame. He just turned 50, has a pleasant rowhouse on Capitol Hill, a longtime spouse, two kids and a teaching gig at George Washington University.

But, in the quiet of the morning, when everyone has left? And he sits in the wing chair beside the baby grand in the front room? Weird stuff starts happening.

On the laptop in front of him, Edgar Allan Poe rises again to confront fictional horrors. So do Sir Walter Raleigh, Christopher Marlowe and Eugène François Vidocq, the Parisian thief who became the father of modern criminology. In Bayard’s (rhymes with “fired”) highly regarded fiction, historical fact and his hothouse imagination run together, creating disturbing worlds that never quite existed.

In the newly released “Roosevelt’s Beast,” for example, Theodore Roosevelt and his adult son Kermit travel on their factual 1913-14 expedition down Brazil’s remote Rio da Duvida, the River of Doubt — but take a fictional three-day detour into nightmare, confronting a never-seen jungle beast that leaves no tracks but disembowels its victims.

“My elevator speech to describe it,” he tells a crowd at One More Page Books in Arlington on a recent evening, “is that it’s Teddy’s Roosevelt’s ‘Heart of Darkness.’ ” (He’ll be on WAMU’s “Diane Rehm Show” Thursday to do the same. Also, it should be noted, he is a frequent book reviewer in these pages.)

The “darkness” line is a tongue-in-cheek nod to Joseph Conrad’s classic novel of white explorers in the 19th-century African Congo — but, like most of his books, a good chunk of Bayard’s novel follows the historical record.

In “Beast,” just as in real life, three of the expedition’s 19 men die and the rest nearly starve. Just as in real life, the former president’s health never recovered and he was dead five years later. And in real life, Kermit Roosevelt — a noted soldier, explorer, author, a friend of Kipling’s and other literary lights of the day — dissolves into depression, drink and suicide.

“It’s a challenge and a kick,” he says, with a laugh, “to put [historical figures] on the page and . . . bend them to my sadistic will.”

Also: “This book is mostly an allegory for depression — the hollowing out of people, it’s what depression does.”

To be the author of such somber material, Bayard is surprisingly good-natured. Tall and thin, he’s funny in person, both at home with reporters and in public with readers. He has been partner/spouse/parent with Don Montuori, a market-research publisher, for more than a quarter-century. He doesn’t bother with the sport-coat-and-tie outfit of the typical Washington author at his public events, instead opting for slacks and a dress shirt. He can talk literature, which he teaches at GW, or he can talk “Sunset Boulevard,” one of his favorite films.

He wrote “Beast” as he does all his books, with beautifully wrought sentences that seem more in the realm of literary fiction than the genre tag of “mystery.”

“It was, after all, a terrible thing to stake all your hopes on love and find even love insufficient.” “When she laughed, she had a way of tilting her head back as if she were imbibing the joke from a great stein. Her hands tilted up, and her long white neck glowed like coral.”

There is also the phantasm-like quality of H.P. Lovecraft. Once “the beast” has taken hold of Kermit Roosevelt, the man’s mind deteriorates, even after the river journey is over, even during routine conversations on Constitution Avenue back in Washington:

“He couldn’t take his eyes away from the senator’s forehead, where a long serrated band of white skin was even now lifting to expose the raw tissue beneath. Before Kermit could intervene, another band of skin peeled off the senator’s aristocratic cheekbone. Then another and another — insult upon insult — until it seemed the senator’s entire head were dissolving, down to the last reddish-white hairs of his beard.”

In his most popular book, 2007’s “The Pale Blue Eye,” Poe is (as in real life) a young cadet at West Point, but helps a detective solve a fictional “suicide” in which the victim’s heart has been removed. “Reads like a lost classic,” said the New York Times Book Review.

In 2009’s “The Black Tower,” Vidocq helps solve a fictional homicide in post-Napoleonic France. “Few writers today can match the author’s skill in devising an intelligent thriller with heart,” Publishers Weekly said.

There are a couple of mysteries to the man himself.

One is how such a funny, outgoing guy (a warmth that was on display when he once won $17,000 on “Jeopardy!”) who is not a historian writes such historically accurate, psychologically acute novels. The second is a question of delayed timing to his career.

The answer to the first is simple:

He does about six months of research for each book, mostly reading, into the settings. He’ll create computer files for major characters and settings. He often travels to the locale in question in search of historical details. He’s been to London and Paris, but skipped the Amazonian rainforest setting of “Beast.” Then, with a good idea of the atmosphere of the era, he sets his historical characters in motion.

The second is more pragmatic:

He was born in Albuquerque, the son of a career Army officer and a British mom who met in Iceland. The family, complete with two older brothers, eventually moved to Springfield, where he graduated from West Springfield High. His high school English teacher, Jill Hilliard, was such an influence that he dedicated “Beast” to her.

He went to Princeton and studied writing under Joyce Carol Oates, who taught him the exacting approach to each word in each sentence, then obtained a master’s degree in journalism from Northwestern University.

And then . . . nothing.

He got “zero offers” in journalism after college. He came back home to D.C. and worked on the Hill in various communication jobs, for former congressman Philip Sharp (D-Ind.) and Del. Eleanor Holmes Norton (D-D.C.). He wrote a pair of modern romantic comedies for a small gay press in Hollywood, but was dismayed to find the books relegated to the “gay/lesbian” sections at the back of bookstores.

“I wanted to be in the front of the bookstore,” he says in a conversation at the dining room table of his house.

So he created a novel that took on his favorite writer, Charles Dickens, and one of Dickens’s most beloved characters, “Tiny Tim” Cratchit, the young hope of “A Christmas Carol.”

Bayard imagined Tim as a dissolute adult in the Victorian age — fog and hansom cabs and the London underworld — and “Mister Timothy,” emerged, a breakout novel that established a new career as half literary fiction, half thriller.

“It’s something we talk about at the store — where do you put the book?” says Eileen McGervy, owner of One More Page. “Louis is a beautiful writer, so when you layer in the historical aspect, it lends more to the novel side of it. But there’s also the mystery aspect, and some readers will tell you they don’t want to read mysteries and they’ll just set it aside.”

There resides Bayard — the man who looked up Kermit Roosevelt’s handwritten diaries of the expedition that helped drive him mad, locked away in the Library of Congress — looking for hints of sanity in the madness of the Victorian realm.