Ruth meets DCI Harry Nelson, who is searching for two missing children, when he finds Bronze Age bones in the marsh. Nelson has also received letters about the missing girls that have references to Norse mythology and archaeology.
I love the ocean, mythology, and anything ancient, so the setting attracted me immediately. As Elly Griffiths explained in an interview:
We were walking over Titchwell Marsh on the North Norfolk coast and [her husband, an archaeologist] happened to mention that prehistoric man saw marshland as sacred – because it’s neither land nor sea but something in-between, they saw it as a kind of bridge to the afterlife. Neither land nor sea, neither life nor death. The entire plot of The Crossing Places came to me in that instant.
The next mystery in the series, Janus Stone, has references to Roman mythology, and Library Journal promises it has more "wonderful British seaside scenery". It will be interesting to see how Ruth and Harry get on in the next novel, given their odd relationship in The Crossing Places.