Constance Sparks always says yes when her capricious best friend needs money; when her boss gives her more responsibility without a raise; and when her boyfriend, Hayden, who is very kind but also secretive, asks her to marry him. While planning their wedding - and struggling with anxiety about the right course for her future - Constance researches the history of her antique engagement ring and unearths the name of a man who might be connected to it, plus his tragic love story. When she finds a book of letters in her library's old manuscript section written by the long-dead man, Constance is deeply touched by his words and leaves a note for him confessing her uncertainty and doubts. She's shocked days later to find a response tucked among the pages. As the notes continue to arrive, Constance finds herself quickly falling in love with a ghost and putting her real-life relationship in jeopardy. Will a bond based on letters impossibly sent from the past derail her future? Or will Constance discover her voice and risk everything for the chance to somehow connect with her true soul mate?