Novelist Daniel Wallace – best known for “Big Fish,” the basis for Tim Burton’s 2003 film – undertakes a striking first venture into nonfiction with “This Isn’t Going to End Well.” A memoir wrapped in an elegy – or maybe the reverse – it states its project crisply: “This is a book about the life and death of William Nealy, my brother-in-law, a man I loved and admired and who left this world, by choice, when he was forty-eight years old.” That clean, clear language, sturdy throughout, is fitting, as it maps a strangely stunning life.

Who was William Nealy? What made him do it? Wallace slowly unravels the fascinating – and ultimately tragic – story of a man who, though very close to Wallace, somehow kept his inmost self hidden in plain sight. Though Nealy is the focus of “This Isn’t Going to End Well,” the book is necessarily Wallace’s story, too, marking his maturation as a man and writer as he works to unpack Nealy’s history.

The tale opens with a literal splash, as Wallace recalls coming home from seventh grade in 1971 to find his big sister’s handsome, fearless boyfriend “standing on the roof . . . eyeing the swimming pool about twenty-five feet below. William.” Young Wallace is stunned. William’s contrasting “wildness . . . derring-do . . . willingness to take flight – literally – into the unknown” had never “been modeled to me by anyone.”

As William jumps successfully – and keeps jumping – Wallace lets himself fantasize from this distance “how the rest of our lives would have turned out had (William) died that day instead of . . . three decades later.” Yet William will continue, “so alive . . . in his leather jacket . . . plain white T-shirt . . . assassin-style sunglasses . . . hair the color of burned butter.” Wallace marvels “that someone so remarkable and dangerous could ever be reduced to ten cups of ashes in a small wooden box.” One hears Hamlet sadly mulling Yorick there.

Early on, William becomes a devoted mate to Wallace’s beautiful sister Holly (more fiercely when her lifelong struggle with severe rheumatoid arthritis begins). As they grow up, William shepherds Wallace through thrilling forays: rock concerts, fishing trips, movies, carpentry, booze, weed. A self-made, hellbent naturalist and survivalist, William stashes weaponry of every sort. But “despite the guns in the secret cutaway wall . . . despite the paramilitary esprit of his imaginary life . . . he never, ever hurt a living soul . . . I thought of him as the child of James Dean, Albert Camus, Ernest Hemingway, Keith Richards, Satan, G.I. Joe, and of course, Clint Eastwood.”

That list makes sense: William, a prolific cartoonist, described himself to an editor as a “Boy Scout . . . high school dropout, war resister, civil rights activist, construction worker, college student, mountain rescue specialist, garbageman . . . rock musician, police analyst, sculptor, spelunker, motorcyclist, bowhunter, paramedic, canoeist, kayaker, river guide . . . parachutist, author . . . yachtsman . . . archer, rollerblader, tree surgeon . . . drunk . . . drug addict.”

Wallace’s book is illustrated with William’s extraordinary cartoons – detailed maps of rivers and back country, white-water guidance, character satires, first-aid instructions including “Swimming Self-rescue.” All are practical yet witty; their exuberant energy reminiscent of R. Crumb’s work. (Many of these marvelous maps and drawings became popular books – a halcyon period for the young iconoclast.)

Wallace chronicles William’s trajectory, including his first encounter with Holly (William is “playing with matches and gasoline,” a perfect prophecy), their wild adventures (motorcycles and sex) and Wallace’s steady wish to emulate his rogue-space-cowboy of a future brother-in-law. “He wanted to get as close as he could to disaster, but then, through wit and skill . . . get right out of it.” When Holly’s illness “turned (her) to stone,” William didn’t leave. “He was a caretaker and a problem-solver . . . he tried to fix it . . . a born adventurer who became a nurse to the woman he loved . . . I think he would do it again.”

By a certain point, the men relate as brothers. “Riding bikes, smoking cigarettes, playing pool, drinking cheap beer . . . brought us close.” But Wallace also consistently questions “how much of it was me and how much of it was me trying to be William.”

What Wallace manages in setting down this cryptic, powerful story is fourfold: He conveys its intense mystery – secret journals and letters show up – in due course revealing what shaped and drove the wounded, gifted young man, from his 1953 birth in Alabama to the end in Virginia, near a houseboat on a lake in 2001. (William) was like Odysseus. Heroic and destructive. Cursed by the gods to be himself.” He evokes the natures of the key players, their feats and their settings in time and place with sensuous immediacy. He describes how it felt to live inside his own, hapless witnessing, and later mortal reflections. “I’m not in the world to break it or to be broken by it.” Above all, he imbues this chronicle with tremendous compassion – for William, for everyone.

“This Isn’t Going to End Well” gives off the particular radiance of a life lived hard, whatever else: as such, a brand of American bildungsroman. There’s deep satisfaction to its arc, despite its inherent sadness – a wondrous glimpse of the melding, in human doings, of fate, character and serendipity.

Joan Frank’s recent books are “Juniper Street: A Novel” and “Late Work: A Literary Autobiography of Love, Loss, and What I Was Reading.”