A life of the mind becomes more momentous for father and daughter David and Ada Sibelius. David’s steadily encroaching Alzheimer’s disease is about to thrust them both to the edge of disaster. Living a secluded life in their old Victorian in Dorchester, a suburb of Boston, David and Ada are mostly happy in each other’s company. While David is content to homeschool his brilliant 12-year-old, Ada is happy to spend her waking hours, giddy with anticipation. completely enamored with her genius father who directs a computer science laboratory at the Boston Institute of Technology.

The novel opens in the 1980s on the night of a celebratory dinner party for David’s best friend and neighbor, Diana Liston. Liston is smart and impressively self-educated, and Ada considers Diana her favorite person in the world; she greedily consume everything that Diana and anyone else tells her. Also present are David’s colleagues from the lab: Hayato, Frank, Joonsong, and Edith. While David frantically cooks a passionate meal, Anna adopts the role of hostess. Together with David, these people are Ada’s constant source of companionship, each offering something necessary to accent her insular existence.

Too often, raven-haired Ada feels like an outsider. The desire to be around kids her own age is always secondary to her urge for self-preservation. For the most part, Ada is utterly content with her strange existence, satisfied with the notion that it is just “Ada and David together always.” Then she notices an abrupt change in David’s disposition. Almost overnight, her father transforms from “the blithe and curious to the concerned and withdrawn.” As a sense of uneasiness creeps into Ada’s daily life, David begins to seclude himself in his makeshift basement laboratory. At dinner each night, he seems distracted, as though he’s caught in a blind mental fog.

In the weeks and months following the dinner party, no one mentions David’s sudden loss of memory. Tall, thin and rigorously possessed--and with a strong background in pure mathematics--David is a proud and able man, unwilling to acknowledge the disease is rolling in like “a powerful foreign front advancing.” David is more concerned with getting his daughter to work at a puzzle disk which contains an application of artificial intelligence, a “chatbot” program called ELIXIR that simulates human conversation. David hopes for ELIXIR to acquire language the same way that a human does.

As David deteriorates, Ada turns to ELIXIR for help, the program providing the spark that ignites Ada’s investigation into her father’s past. She knows little of his childhood, so Ada turns to Liston for help. At first Ada rails against David’s betrayal of her trust, but then she grows wary, pacified by Liston’s excuses. The more Ada researches her prodigal father, the less of his life she feels to be understandable and true. As Ada’s questions grow in number, she undertakes an intensive investigation of David’s possessions, discovering a litany of her father’s many half-truths and deceptions: “he was open to others but never with her.”

Moore works her literary magic, unfolding Ada’s first days at the Queen of Angels School where she she is forced into a painful and uncomfortable existence, ignored by her classmates. After David is institutionalized, she finds herself living with Liston and her five children. William, the eldest son, becomes Ada’s first crush, while introverted Gregory takes a shine to her. He’s a year younger than Ada and is perhaps the most difficult of the brothers to understand. Moore traces Ada’s attempts to juggle her newly-adopted family with her father’s endless battle with dementia. The author’s detailed account of Ada’s struggle to piece together David’s puzzle is vigorously melded with Ada’s life in Palo Alto in 2009, where she faces pain and bewilderment in dealing with her personal relationships and work dilemmas.

While the mystery behind David’s shadowy past drives us to turn the pages, some readers might struggle to engage with the novel’s more mathematical elements, especially David’s ELIXIR riddle and Ada’s own research into alternative reality and artificial intelligence. Ada’s yearnings--etched in absolute clarity--give real meat to the story, providing a definitive account of how she deals with life and its bitter cravings. Ready to rewrite her own version of her history, Ada will gradually come to reflect on this most precious of unseen worlds, the unassailable connection between a father and her daughter.