Quite a few things go out the window in “The Defenestration of Bob T. Hash III” (Random House, 242 pages, $22), but you will find no spoiler here telling whether Bob T. Hash III is, as the novel’s title suggests, one of them.

This sly and discombobulating flight of whimsy by David Deans is, in a sense, a book-length joke, and nothing drains the humor from a good joke as effectively as vivisecting it. Detailing Mr. Deans’s plot, too, is risky. He has set this persistently funny metafiction inside the world of an Acme foreign-language picture book called “Forward with English!”: a world that’s “all very modern in that retro, stuck-in-a late-1950s-early-1960s-time-warp course-book kind of way.” In the role of narrator is the Hash family parrot, Comenius, an African gray who falls off his living room perch in a spray of birdseed one day and picks himself up only to discover that he’s metamorphosed into the innocuously handsome man of the house, Bob T. Hash III, aka the protagonist of “Forward with English!”

So, out the window immediately: logic, laws of nature, and, evidently, any chance of hooking the reader with a sexy premise. What remains is Seussian, Pirandellian lunacy, related with a poker face.

Bob T. Hash III, his demurely alluring wife Matilda, their three largely irrelevant children, and their indispensable parrot live in the picture-book town of Belmont, which apparently is in America (among other scraps of evidence: One can drive there from Canada), though closets are routinely referred to as cupboards, fedoras are often called trilbies, and the temperature is given in Celsius. Such shifting of ground and blurring of certainties is emblematic of the prankish chaos Mr. Deans sows throughout.

The town is idyllic in the bland, stilted, scripted manner of “The Truman Show” and “Pleasantville,” or perhaps “Leave It to Beaver,” if the focus were on Ward, June, and the pet bird who’s become Ward’s doppelgänger and, in his adoration, made June feel like a new woman. Except, of course, that it’s difficult to imagine Ward and June naming their parrot after the 17th-century Czech J.A. Comenius, an influential language educator and a pioneer of the illustrated textbook. But such is the winking nature of Mr. Deans’s tale. (Another wink, slightly unsettling because it’s so unnecessary, is the likening of Bob’s affable air to that of “a youthfully middle-aged Robert Lowell who, laying aside a tortured poem on the weekend and throwing off his cardigan, might play Frisbee on the lawn with his children.” Lowell is famously linked with another Belmont, the one in Massachusetts, where he was several times a psychiatric inpatient at McLean Hospital.)

As Comenius explains, Bob T. Hash III, though the star of “Forward with English!” and therefore Belmont’s most prominent citizen, eventually finds his picture-book existence too constricting to bear. At Belmont International Airport, where he is supposed to be catching a flight for a daylong business trip, he absconds to Acapulco with his secretary and paramour, Miss Scarlett. Meanwhile, Comenius slips into Bob’s shoes — as well as his suit, his hat, his job, and his family. It’s a thrilling adventure for a creature who’s spent most of his life playing with bird toys, and an easy task for a mimic. Only Matilda seems to detect a difference, and she’s delighted.

It’s at work that the earnest and erudite Comenius discovers something that scandalizes him in the manuscript Bob has written for the new, eighth edition of “Forward with English!” The pages are rife with willfully nonsensical mistranslations, mischievously dreadful social advice, and subversively unhelpful role-playing exercises, all of them meant to be on their way to the printer. Bob T. Hash III, it seems, is not the upright man he’d appeared to be. Comenius sets out to rescue the eighth edition, spurred by his own sense of grammatical propriety and by the knowledge that he, now in the guise of Bob and with no way to undo his metamorphosis, is in danger of taking the fall for what he calls Bob’s “glossy derangements.”

As quests go, the one Comenius undertakes could hardly be less glorious, but Mr. Deans — a Scot living in Italy, whose CV includes years of teaching English as a second language — invests it with genuine comic tension. He alternates the parrot’s story with chapters of Bob’s “apocryphal grammar primer,” and the two texts comment on each other, growing contemptuous, threatened (Bob is not pleased at being cuckolded), and threatening (there is some mortal peril).

Or is this all a sham? Has Comenius hallucinated his transformation —and if so, where did he acquire his knowledge of Kafka and Rilke, of Orpheus and Lady Macbeth? Is Bob a good guy after all? Is he even out of town, let alone in Mexico? And where is Miss Scarlett, anyway?

Mr. Deans may or may not provide the answers to these queries. But the reader’s irresistible desire to know is evidence that he’s pulled off a splendid joke.