In this unforgettable novel by the bestselling author of Water Moon, a young Isaac Newton falls in love with a girl living in modern-day San Francisco, defying the laws of physics to forge a seemingly impossible connection.

Andrea Louviere is seven years old the first time he appears. While she’s alone in her bedroom, practicing her beloved cello, the light shivers and a crack forms in the wall. Through the crack, she sees a candle, a window, a desk—and a boy. In the eerie silence, the boy clearly sees Andrea too. Then, as quickly as it opened, the crack closes and he vanishes.

Over the years, summoning the boy becomes an obsession for Andrea. On her seventeenth birthday, she receives a three-hundred-year-old love letter from Isaac Newton. Andrea knows that Isaac will change the world with his groundbreaking discoveries; the letter tells Andrea that she will change him.

As Isaac’s letters intensify in passion and intimacy, Andrea grows determined to follow his clues to their shared destiny—despite a burgeoning romance in the present. Only when she discovers the way into Isaac’s time does Andrea realize that she faces a heartbreaking decision between what was . . . and what might be.