Dr Ruth Galloway is in her late 30s. When she's not digging up bones or other ancient objects, she lectures at a university in Norfolk. She lives alone, content, in a bleak, marshy area called Saltmarsh, overlooking the sea and Norfolk's vast skies, with her cats and Radio 4 for company. She's a salty, quirky character. When a child's bones are found in the marshes near a dig that Ruth and her former boyfriend Peter worked on ten years earlier, Ruth is called upon to date them. They turn out to be Bronze Age bones, and DCI Harry Nelson, who asked for Ruth's help, is disappointed: he had hoped they would be the bones of a child called Lucy, who has been missing and presumed dead for ten years. He has been receiving odd letters about her ever since—letters with references to ritual and sacrifice and quotes from the Bible and Shakespeare. Then a second girl goes missing, and Nelson gets another letter like the ones about Lucy. Is it the same killer? Is it a ritual murder linked in some way to the site near Ruth's remote home? Then one of Ruth's cats is killed, and it becomes clear she's in danger from a killer who knows that her expert knowledge is being used to help the police with their enquiries.