Artie Dam is living a double life. He spends his days teaching history to eleventh graders, expanding their young minds, correcting their casual cruelties, and lending a kind word to those who need it most. He goes to holiday parties with his wife of three decades, makes small talk with neighbors, and, on weekends, takes his sailboat out on the beautiful Massachusetts Bay. He is, by all appearances, present and alive. But inside, Artie is plagued by feelings of isolation. He looks out at a world gone mad—at himself and the people around him—and turns a question over and over in his mind: How is it that we know so little about one another, even those closest to us?

And then, one day, Artie learns that life has been keeping a secret from him, one that threatens to upend his entire world. Once he learns it, he is forced to chart a new course, to reconsider the relationships he holds most dear—and to make peace with the mysteries at the heart of our existence.