When he returned to writing, he did so at full throttle. Foremost of course there was “Lolita,” his “enormous, mysterious, heartbreaking novel,” as the author described it in a letter to Katharine White, his editor at The New Yorker; other books from this period were “Bend Sinister,” “Pnin” and “Speak, Memory.” It took Nabokov five years to write “Lolita,” during which time he was also teaching at Cornell, translating Pushkin’s “Eugene Onegin” and traveling during the summers across the American West by car, chauffeured first by friends and then by Véra, and accompanied by their young son, Dmitri. These vacations centered on the writer’s beloved ­butterfly-collecting — Nabokov was an ardent lepidopterist, having begun to make notes (in English) about butterflies already as a boy in Russia, and with specialized knowledge of a subfamily known as the blues. But these road trips, eventually adding up to 200,000 miles, also enabled him to enter the postwar American landscape, literally and imaginatively, with “a vagabond’s sharp-sightedness.” As Roper explains: “Something miraculous happened. In the late ’40s, the émigré who was finally in command of wise, precise, plastic English took a further step. He undertook the American subject as he saw it.”

In a way, this most sophisticated and supercilious of Europeans, “the beneficiary of a superb Old World education, fluent on the most rarefied levels in three languages,” had been preparing for his encounter with the American mundane for much of his life — an encounter that changed his fortunes from being a penniless writer of radiant but obscure novels to becoming “the most famous literary writer in English in the world.” He had learned to read English by the age of 4 and dreamed of escaping to “vulgar, far-flung America” long before he arrived, immersing himself in native writing (“a second-rate affair in Nabokov’s eyes, although not without interest”) and corresponding with American friends and his American agent, Altagracia de Jannelli, from his perch first in Berlin and then from various small villages in France, finally landing in Paris. When not busy writing his last Russian novels he canvassed for a job, observing to a professor acquaintance that he was not “afraid of living in the American boondocks.” Indeed, in a letter to Jannelli, Nabokov claimed to find something alluringly retrograde about America, almost despite himself: “It may be curious,” he wrote, “but what charms me personally about American civilization is exactly that old-world touch, that old-fashioned something which clings to it despite the hard glitter and hectic night life and up-to-date ­bathrooms.”

As it was, the Nabokovs had nearly not made it out of Europe in time — Roper acutely characterizes them as “Zelig-like figures of 20th-century catastrophe, dispossessed of their native Russia by the Bolsheviks, hair’s-breadth escapees of the Nazis in Berlin and Paris” — but managed to leave on one of the last French ships bound for New York in May 1940. Stanford had offered Nabokov a teaching position (a Russian literary course and one in playwriting, “for a fee of $750 plus accommodations”), and in the fall of that year he met up with Edmund Wilson, the doyen of literary critics and also an uncommonly generous facilitator of writing assignments and jobs. The two became fast friends despite potentially explosive differences in opinion on figures both political (Lenin) and writerly (Faulkner); Wilson, then an editor at The New Republic, offered Nabokov books to review and helped put him in touch with other publishing contacts.

The first of the Nabokovs’ many road trips, sedulously tracked by Roper, who himself “traveled several thousand miles in the East and West,” in search of the writer’s “favorite motel from the summer of ’52,” took place in May 1941 and “established the template for the summer explorations to come”: They set out on a three-week trip to California in a Pontiac driven by one of Nabokov’s language students, traveling until evening, when they checked into one of the motels they favored. Along the way, they visited many parks, where Nabokov “collected madly” when he was not studying road maps or AAA guides — where, Roper observes, “his penciled comments about establishments frequented . . . suggest an embryonic form of the parody of motel names to appear one day in ‘Lolita.’ ”

“Nabokov in America” keeps a close (and, for this nondriver, occasionally tedious) eye on the itinerary the Nabokovs followed on their road tour of the West, the better to familiarize the reader with Nabokov’s unexpected feel for the American parlance, the “vital and vulgar” New World he embraced in part to burlesque it in the pages of “Lolita.” Determined not to entangle himself in the vast edifice of documentation that has grown around Nabokov, Roper casts his account as a travelogue, one that is also a work of serious criticism, while bringing us singularly close to this writer, his indefatigable and endlessly capable wife, and their talented but restless son. (In one of many original insights, Roper suggests that the “magnetically self-possessed” Dmitri was the lucky sibling of Lolita, one whose overprotective parents made sure he didn’t get lost in the maw of predation that closes over the doomed nymphet.)