Ethan is an exceptionally gifted young boy, obsessed with physics and astronomy. His single mother Claire is fiercely protective of her brilliant, vulnerable son. But she can't shield him forever from learning the truth about what happened to him when he was a baby; why Mark had to leave them all those years ago. Now age twelve, Ethan is increasingly curious about his past, especially his father's absence in his life. When he intercepts a letter to Claire from Mark, he opens a lifetime of feelings that, like gravity, will pull the three together again. Relativity is a tender and triumphant story about unbreakable bonds, irreversible acts, and testing the limits of love and forgiveness.