Phoebe Bristow has spent a decade guarding her heart after her father walked out and shattered her family. When she touches a mysterious antique mailbox aboard a whale-watching cruise in Baja California and wakes up in Civil War St. Louis, she must learn to trust again, first the quick-witted man who greets her on shore, then the God who placed her there for reasons she cannot yet understand. Back on the cruise, her mother Erica clings to the mailbox as the only thread connecting her to her missing daughter, while a thoughtful marine biologist, Rodney Duncan, steadily dismantles the walls around her wounded heart. Together and apart, mother and daughter discover that the courage to love again may be the most dangerous mission of all.