Twelve-year-old Ada Sibelius is an unconventional child in an unconventional family. Her father, David, is a brilliant, socially awkward computer scientist. Permanently single, he had his only child late in life, via a surrogate, and now, in mid-1980s Boston, father and daughter form a quirkily symbiotic pair. Ada --- named after famed computer science pioneer Ada Lovelace --- grows up not on the playground or in the schoolroom but in her father’s lab, where his research focuses on natural language processing. The Steiner Lab’s pet project is an artificial intelligence program named ELIXIR, which David and his colleagues hope will eventually be able to replicate human conversation.

Smart, sensitive and almost preternaturally observant, Ada narrates the bulk of Liz Moore’s third novel, an engrossing exploration of family, identity and memory. David’s idiosyncratic approach to Ada’s education means that she knows a great deal about science and math, and has already read ONE HUNDRED YEARS OF SOLITUDE, but is woefully out of her depth when it comes to dealing with her peers. Now on the cusp of young adulthood, she has realized that her father is, in many ways, deeply weird, and has begun to long for the kind of normalcy David abhors.

Ada’s desire for a conventional existence goes unfulfilled. At a dinner party, David uncharacteristically forgets the solution to his favorite logic problem. Readers will immediately suspect what Ada learns only later: Her cerebral father is in the early stages of Alzheimer’s. Already accustomed to being treated more like David’s peer than his child, she bravely takes on the mantle of caregiver while also adjusting to life at the Catholic grade school where she is now a student. But her father’s condition deteriorates rapidly; in a matter of months, David is in a nursing home while Ada has moved in with his colleague, Diana Liston, and her children.

"Moore has deftly combined family drama, mystery and science fiction in this utterly engrossing book."

Watching David’s mental decline unmoors Ada, but worse is yet to come. Even before his illness, there are hints that her father has secrets --- he is estranged from his upper crust New York family, refuses to be photographed, and is “private about his personal life to an extreme.” Eventually, Ada learns that her father, who she admires more than anyone else in the world, may not be who he says he is, which sends her “into a spiral of doubt and pain so profound that it threatened to fell her.”

With the help of a kind-hearted librarian and Liston’s son, Gregory, Ada is able to uncover some scattered facts about David’s past, but the information only raises more questions. The biggest clue he left her before his mind failed completely --- a floppy disk containing a short, encrypted message --- yields no answers, since neither Ada nor his colleagues can break the code.

THE UNSEEN WORLD opens with an epigraph from Alan Turing, and the parallels between the famed World War II-era code breaker and David are numerous. Like Turing, David keeps his true self hidden in a world that is unaccepting of difference, and he is obsessed with codes and fascinated by the idea of artificial intelligence. Yet David is able to take his work on AI several steps farther than Turing ever could. His legacy to Ada includes a hundred pages of source code for The Unseen World, an early virtual reality program. The program inspires Ada’s own work, and by 2009, she has developed a more robust alternative reality software. That, combined with ELIXIR, which is still puttering away in David’s old lab decades after his death, puts Ada on the path to finally discovering the truth about her father.

Moore has deftly combined family drama, mystery and science fiction in this utterly engrossing book. While David’s big secret isn’t difficult to figure out, the real joy and heartbreak is in watching as Ada learns to navigate a confusing world without her beloved parent. In this, she is not too far removed from ELIXIR, David’s other creation; both learn how to interact with people through a painstaking process of trial and error. (David describes his daughter as “more machine than human.”) The youthful Ada, with her tentative and painful explorations of the social minefield that is junior high, is so vividly and sensitively drawn that adult Ada can only disappoint, especially since her appearances are so brief that she is more shadow than fully realized character.

Not everyone will love the novel’s final pages, which venture into the realm of pure science fiction. Moore gambles in moving beyond the universe inhabited by her protagonists, but it’s a risk that succeeds. In taking it, she makes a powerful statement about the power of memory and storytelling, and posits a future where the dividing line between people and technology seems to have vanished almost entirely. To some, that might sound dystopian, but to Moore, it’s a hopeful vision of a world where we all live on, in a way, through our machines.