The Mongol Derby has only been around since 2009, but it immediately garnered and continues to hold the reputation of being the most grueling long-distance horse race on the planet. Following the route of the postal service that Genghis Khan established in 1224, riders traverse 1,000 kilometers across the sparsely populated Central Asian steppes, swapping their semi-wild horses every 40 kilometers and sleeping at stations staffed by local nomadic herding families.

Far from favored to win, 19-year-old Lara Prior-Palmer entered the 2013 race on a whim after finishing high school in her home country of England, when she was floating "in a debris of possible dates and implausible plans, with neither the funding nor the fervor to propel me onward."

"Rough Magic: Riding the World's Loneliest Horse Race" is her gripping, self-searching, triumphant debut memoir about her successful effort to become the youngest rider and the first woman ever to win.

An almost delusionally underprepared underdog, Prior-Palmer lies about her skills, name-drops her equestrian aunt Lucinda Green, gets the "phenomenal entry fee" reduced by over half, and shortly thereafter is off to Ulaanbaatar. Because any reader is going to know the race's outcome upon picking the book up, the interest lies not in the ending, but in how Prior-Palmer gets there.

Luckily, she's an adept storyteller and a humble autobiographer, not afraid to let herself look unlikable or even obnoxious if the circumstances merit. "My thighs were strong and my heart was raw, yearning for my own motion," she writes; the winning vulnerability on display there and throughout this exceptional coming-of-age tale keeps the pages turning and the reader rooting for this unlikely heroine.

A dreamy and peculiar person, Prior-Palmer totes a copy of Shakespeare's "The Tempest" with her because she likes to dive "into the lines for comfort." She observes of herself and her fellow riders: "I believe we sought some kind of oblivion. The characters in 'The Tempest' leap from their sinking ship in a 'fever of mad.' "

Prior-Palmer's own arguable madness aside, the animals involved are sanely and humanely looked after. She notes that the rules impose a two-hour penalty or race expulsion "if a horse's heart rate remained above 64 beats per minute for a period longer than 45 minutes at the end of each leg," a detail that will become vital later on (but which would be a spoiler to say more about).

The camaraderie and competition she experiences, particularly with American front-runner Devan Horn, and the dynamic she establishes with the horses who remind her that "animals were our first teachers" make this memoir a breathtaking ride, rich with "meaning beyond victory vs. loss."

Kathleen Rooney is the author, most recently, of the novel "Lillian Boxfish Takes a Walk" and "The Listening Room: A Novel of Georgette and Loulou Magritte."

Rough Magic
By: Lara Prior-Palmer.
Publisher: Catapult, 274 pages, $25.