In the dim morning light, Orkney’s Skaill Bay is the backdrop for a calamity of nature’s making. When forensic scientist Rhona MacLeod joins the rescue efforts as a volunteer, she uncovers more than she bargained for: a human skeleton entombed in a stone crypt. The grave is believed to hail from the Viking Age, but Rhona's analysis of the content points to more recent and sinister evil.

And a shadow is thrown over the investigation when the skeleton is finally identified – and unsettling connections emerge between the victim and the very people trying to solve. As forensic clues lead Rhona to a second, horrifying discovery, the question looms: how many more secrets are concealed in the sand?