As David Sibelius boils the lobsters for the annual dinner he hosts for his graduate students at the Boston Institute of Technology, his 12-year-old daughter, Ada, observes him with a sense of foreboding. “She could not articulate what was different in his demeanor, but it triggered a deep-seated uneasiness in her,” writes Liz Moore in her enthralling new novel, “The Unseen World.” Ada will soon learn that her brilliant, enigmatic computer-scientist father is in the early stages of Alzheimer’s disease.

(W.W. Norton)

Later that evening, David, who still has the presence of mind to know that he is faltering, gives Ada a floppy disc, encased in a white plastic clamshell. On the disc is a curious string of code that will take Ada more than two decades to decrypt: It will unlock dark secrets from David’s past and provide the key to “The Unseen World.”

Set in the 1980s in the pre-Internet days of the emergence of artificial intelligence, this is a novel that artfully straddles genres. It is a rich and convincing period piece that captures daily life in the modest neighborhood of Dorchester in an era of wall-mounted phones, frozen Salisbury steak dinners and first-generation home computers, like Ada’s 128K Macintosh, which boots up with a question mark without its operating system disc inserted, as if “its mind was missing from its body.”

But “The Unseen World” is also a cerebral, page-turning thriller, a novel about code that is itself written in a kind of code. Traversing time, it takes us back to Kansas in the 1920s, skips ahead to San Francisco in 2009 where Ada works for a tech firm, and then projects briefly a sci-fi-ish glimpse of the future.

Ada is a quiet, brainy, observant child who was birthed by a surrogate, raised by a single father and home-schooled — or really “lab schooled” since she accompanies David to work at the Steiner lab most days. She works on David’s project, ELIXIR, a chatbot program aimed at simulating human conversation. Ada is asked to converse with ELIXIR to help it acquire language. The program is designed to be continuously self-teaching, “to attain more intelligence with each conversation it conducted.”

Ada is well suited to this task. “You are more machine than human,” her father says at times. She does not disagree. “ELIXIR triggered Ada’s emotions in unexpected ways. . . . It brought out the same warm feelings in Ada that a friend might have.”

Author Liz Moore ( Olivia Valentine)

Once David is no longer able to care for her, however, Ada is thrust into the more corporal world. She moves in with the family of her father’s close colleague Liston and is enrolled in the eighth grade at a Catholic school run by mean nuns. It is a rough transition for Ada, who shows up the first day unaware of school rules or teen etiquette, and she finds herself fantasizing about “what it would be like to be amorphous.” She continues to sneak back into her father’s house where she converses with ELIXIR. It’s a way to stay connected to her former life, and many years later she will again turn to ELIXIR to help finally solve the riddle of her father’s life.

Language in this novel is sensual and precise starting with the critical opening dinner party scene: “The light that day was the color of honey or of a roan horse, any warm organic thing like that, coming through the leaves of the tree outside the window in handsome dapples, lighting parts of the countertop generously, leaving others blue.” The clarity of this scene will come back to haunt and demand to be reread through the newly acquired lens of the novel’s epilogue.

There is, however, sometimes an overabundance of detail that threatens the otherwise sharp narrative. Ada’s awkwardness in school — her brainy-kid-with-glasses take on the popular girls, her desire for pierced ears — begins to feel unnecessary and veers toward cliche. And David’s backstory is arguably more elaborate than it needs to be, causing the book to occasionally sag.

But these are minor complaints in what is otherwise an elegant and ethereal novel about identity and the dawn of artificial intelligence, and a convincing interior portrait of a young woman, “a shadow-girl who could slip imperceptibly around corners and through hallways,” who is conversant in worlds both seen and unseen.

Susan Coll is the author of five novels, most recently “The Stager.”

The Unseen World

By Liz Moore

W.W. Norton. 451 pp. $26.95