In “The Mistress’s Daughter” (Viking, 238 pages, $24.95), A.M. Homes, one of fiction’s more masterly chroniclers of suburban ennui, has turned her unsparing lens on the substance of her own life. This new memoir, a fleshed out and much expanded version of Ms. Homes’s 2004 New Yorker essay of the same title, traces her encounter with her biological parents 31 years after they gave her up for adoption.

It is a strange tale, rendered stranger still by Ms. Homes’s singular ability to capture the workings of her own consciousness. The lurking possibility that the past of an adoptee will resurface at random is — at least in the age of genetics and Google — built into the nature of the undertaking, but Ms. Homes plumbs the question of her identity to its roots (and not simply in the politically correct, multi-hyphenated sense of the term.) What really interests her are the ineffable details of our biological inheritance. Put simply, she is deeply attuned to the weirdness of her situation: “I am on the phone talking to my mother when she gets a call telling her that my mother is dead. It’s a little too much like a Gertrude Stein line,” Ms. Homes reflects upon learning from her adopted mother that Ellen, her biological mother, has died.

Ms. Homes is fascinated by the bizarre duality of living a life with a counterfactual existence buried beneath it. What begins as an inquiry ends as obsession. And who can blame her? When her biological mother tries to contact her via her lawyer, an entire history, once relegated to the realm of mystery, starts to take shape. Ellen barrels into her life eager to make up for lost time, assuming instantly the role of the needy parent. “I’m angry with you, can you tell?” she demands aggressively when Ms. Homes neglects to call on Valentine’s Day. Ms. Homes’s portrait is hardly sympathetic, but the very force of “The Mistress’s Daughter” derives from the sense that Ms. Homes doesn’t seem to have enough distance from the whole affair to temper her instincts in the interest of evenhandedness.

Her biological father gets the better bargain in this equation, at least initially. Perhaps because their physical resemblance is harder to ignore, Ms. Homes laps up his promises to incorporate her into his family, even as she denies affection to her clingy mother. In one of the memoir’s most startling scenes, the surreality of Ms. Homes’s position strikes us fully as her father stands up to take a paternity test. “As Norman walks to the counter,” Ms. Homes observes, “I notice that his butt looks familiar; I am watching him and I am thinking: There goes my ass. That’s my ass walking away. … This is the first time I have seen anyone else in my body.”

Such refusal to shy away from the seedier underpinnings of both relationships lends the first half of the memoir its integrity. Short stories are Ms. Homes’s most effective form, and “The Mistress’s Daughter” hits hardest when it compresses the explosion of a moment’s intensity into a single, concentrated detail — the pants with creases that mirror the body of their dead owner, the recognizable ass moving away. Though Ms. Homes’s reliance on present tense narration and rhetorical questions gets relentless at times, she succeeds in conjuring up a tone of desperation: We believe that her whole identity is at stake.

Unfortunately, this feeling of urgency lapses in the book’s later chapters. The narrative begins to lose its thread when Ms. Homes forgoes the immediacy of storytelling and starts digging for answers. As she recounts her efforts to unearth more information about her background, she breaks the story down into choppy sections that are less cohesive, and less powerful, than the opening segment.

The chapter “The Electronic Anthropologist” traces her genealogy with a level of detail we might apply to the royal family. Another, “Unpacking My Mother,” trespasses on the boundary between the real and the imagined in order to envision Ellen’s life through her own eyes. Ms. Homes’s sense of economy, so critical to the story’s emotional heft, all but disappears in a section devoted to a hypothetical interrogation of her father, a string of entreaties issued by an invisible attorney that sounds suspiciously like padding. For all the memoir’s persistent questioning, there are nonetheless some holes. Where, for instance, are her adopted parents in all this? They hover in the background throughout, but only as shadows, never as real as her “real” parents.

While these digressions and flights of fancy don’t exactly make for an ordered narrative, Ms. Homes succeeds in communicating the visceral nature of her experiences, perhaps more so for her clumsiness. Ms. Homes, it appears, is still working out the intricacies of what it means to have a tangible past — a personal history — on the page, and for that “The Mistress’s Daughter” is less an answer to the question of what it means to be adopted than an articulation of its unsolvable dilemmas.

Ms. Atlas last wrote for these pages on Tracy Chevalier’s novel “Burning Bright.”