Half of the novel is historical fiction based on the Smuttynose Island murders, which took place in 1873.

In March 1873, two Norwegian-born women who lived on the desolate Smuttynose Island, one of the Isles of Shoals off the coast of Maine and New Hampshire, were brutally murdered.

Maren Hontvedt, a sister of one of the victims, survived by hiding in a sea cave until dawn.

More than a century later, Jean Janes, a magazine photographer working on a photo essay about the murders, returns to the Isles with her husband Thomas and five-year-old daughter.

Hoping to have a small vacation, they travel on a boat skippered by Thomas' brother Rich, who has brought along his girlfriend Adaline.