On a dreary September morning, Dave Sanders's life turns upside down when his missing son, Eli, appears on his doorstep. Missing for fourteen years, Eli's reappearance forces Dave to re-live the moment his wife ran off with their son, and abandoned their daughter, Abby. As Dave navigates both his and Abby's resurgence of grief, the questions as to why his wife left and where she is now resurface, and Eli's reappearance isn't the only surprise in store for him.

Abby has forgotten much about her baby brother. He was nothing more than a bald head and a baby's giggle when their mother chose to take him with her and leave Abby behind. For most of her life, Abby has been angry at her mother and all of the milestones she's had to navigate without her-buying her first bra, learning how to use makeup, her first kiss-milestones that were meant to be between mothers and daughters. Now, with the tragic news that Eli brings with him, Abby has the choice to let the anger fester within her or to finally make peace with what is in the past.

A story of love, hope, and heartache, Letters to Abby follows Dave and Abby as they rebuild their family after post-partum depression tears it apart.