U.S. author Joshua Ferris ventures into dark, daring terrain with his new existential novel The Unnamed. (Nina Subin/Hachette Book Group Canada)

Joshua Ferris's latest novel, The Unnamed, keeps readers off balance from the start. In the gripping opening, lawyer and protagonist Tim Farnsworth travels home from work, chauffeured by an unknown driver. As he watches the passing scenery, his narration offers clues that something is amiss — he mentions the return of frostbite and observes that he is "going to lose the house and everything in it." Once he arrives at home, Tim strips off his suit, turns to his wife, Jane, and announces: "It's back."

In The Unnamed, you don't know whether the main character's agonizing malady is physical or the result of a devastating nervous breakdown.

"It" turns out to be the vague illness alluded to in the book's menacing title. Once Tim is in its grip, he has no self-control. He simply stands up and walks — out of a courtroom in the midst of a trial, for example, or out of his bedroom in the black of night. He keeps on walking for marathon distances, until he collapses into a bone-weary sleep. Doctors from Rochester to Switzerland have poked, prodded and scanned Tim's brain, but no one (not even the New England Journal of Medicine) has any answers about his bizarre compulsion.

This unsettling premise is a far cry from Ferris's darkly funny 2007 debut, Then We Came to the End, a satirical look at a bunch of office drones facing layoffs at a Chicago ad agency. During a recent phone interview from his home in upstate New York, the award-winning author acknowledges The Unnamed's more serious tone.

"I had to show restraint, comedic restraint, which is not a natural inclination," Ferris says about the writing of his newest novel. "There's a way to tell the story that seems organic and natural, and to abide by the rules of that is the more respectful approach. If I had attempted to be comedic in the same way that I was with Then We Came to the End, I would have done the subject matter of The Unnamed a disservice."

Ferris is an author who feels his way into his material. "There's no outlining, there's no pre-planning, there's no guidebook. I'm finding [the story] sentence by sentence," he says of his craft. This gut-instinct approach creates a delicious ambiguity that Ferris manages to sustain throughout The Unnamed — as a reader, you're uncertain from chapter to chapter whether Tim's agonizing malady is physical or the result of a devastating nervous breakdown.

Determined to go wherever his story leads him, Ferris winds up in dark terrain, where the crack-up theory becomes increasingly feasible. The book's daring second half features time shifts, hallucinations and some horrific passages in which Tim succumbs to wild ravings as he argues with "the other" that's taken hold of his body. It's a disorienting risk that yields some weighty, challenging questions about God and the soul. Ferris says he's been preoccupied with existentialist ideas since studying "hardcore" philosophers like Heidegger and Husserl as an undergraduate.

(Hachette Book Group Canada)

Clearly turned on by ideas and language, Ferris is an expansive, erudite interview subject. In the midst of a mesmerizing discourse on American poetry, Ferris enthuses about Emily Dickinson, whom he considers "the most eloquent poet with respect to suffering, and the way in which grace can be derived from suffering."

Lines from Dickinson's verse After great pain, a formal feeling comes provide the titles for the four sections that make up The Unnamed's narrative. Ferris acknowledges her influence on the novel. "She is always vacillating between faith and doubt and relief and suffering and love and loss, so in some ways she was the prevailing spirit of the book."

Ferris achieves the same balance in his novel, displaying a keen instinct for when to deliver moments of relief amidst the despair. In the rare instances when Tim isn't in motion, he experiences quiet, powerful joys — sharing a beer with the compassionate security guard at his work, bonding with his teenaged daughter over Buffy the Vampire Slayer, or indulging in a furtive hospital-room tryst with Jane.

The novel's most stirring moments lie in the examination of Tim and Jane's marriage, a union tested after both discover they've signed up for more sickness than health. Ferris admits that for him, the couple's enduring bond is what the book is all about. "I wanted to ask the question: What's essential in his life? And everything falls away except for Jane."

This love story helps to propel readers through the novel's severe final stages, as Tim's restless limbs carry him across a punishing, indifferent American landscape, and conventional plotting gives way to ruminations on decay, suffering and finally grace. The Unnamed is an admirably ambitious novel, rewarding for its steadfast refusal to be light bedtime reading.

"There's such enormous pleasure for me, when I'm reading something that really resists assimilation, and suddenly — either through my diligence or perseverance — it breaks through and meaning is resolved," says Ferris.

"[With The Unnamed], I am attempting in a much more aggressive way to challenge the reader, and to allow for the reader's active participation in something that will eventually yield the kind of pleasure that I'm aiming for. It's an earned pleasure, but I find it to be as meaningful, if not more so, than the kind of pleasure that you get from something that is easier to understand."

The Unnamed is in stores now.

Lee Ferguson writes about the arts for CBC News.