The Crossing Places by Elly Griffiths

A child's bones are discovered on the windswept Norfolk marshes. Believing them to be ancient, the police call in Dr Ruth Galloway, forensic archaeologist. But this is no prehistoric grave. A cold missing person case has now become a murder investigation.

Dr Ruth Galloway is called in when a child's bones are discovered near the site of a prehistoric henge on the north Norfolk salt marshes. Are they the remains of a local girl who disappeared ten years earlier - or are the bones much older?

DCI Harry Nelson refuses to give up the hunt for the missing girl. Since she vanished, someone has been sending him bizarre anonymous notes about ritual sacrifice, quoting Shakespeare and the Bible. He knows that Ruth's expertise and experience could help him finally to put this case to rest.

But when a second child goes missing, Ruth finds herself in danger from a killer who knows she's getting ever closer to the truth...