1949: During the coldest winter Seattle has seen in decades, pregnant sixteen-year-old Brigid Ryan arrives at Fairmile, a home for "fallen women" run by the Catholic Church on a remote island in Puget Sound. She and her baby will disappear before the snow melts.

2013: Ex-cop Frankie Gray is escaping a career in ruins and hoping to reconnect with her teenage daughter, Izzy, while summering with her mother at The Fairmile Inn, soon to be a boutique hotel. But when an elderly nun who worked at the home in its former iteration is found dead in suspicious circumstances and then a tiny skeleton is discovered on the grounds nearby, Frankie goes looking for answers. Then Izzy disappears, and as Frankie races to find her, she turns up a secret that will force her to question her own history and the identity she thought she knew.

Over sixty years separate the disappearances at the Fairmile, but Frankie suspects that they may share the same dark root; in the suspenseful, atmospheric investigation that follows, she finds that the truth is as foggy as the rocky, isolated island on which that darkness thrived.