The Saltmarsh and its henge are completely imaginary.
There was, however, a bronze-age henge found in North Norfolk, at Holme-next-the-Sea. For descriptions of this henge I am indebted to Francis Pryor's marvellous book Seahenge (HarperCollins).
The University of North Norfolk and the King's Lynn police force are also entirely fictional. Thanks to Derek Hoey and Graham Ranger for their insights into modern policing and to Michael Whitehead for supplying the Blackpool background. I am also grateful to Andrew Maxted and Lucy Sibun for their archaeological expertise.
However, in all these cases, I have taken the experts' advice only as far as it suits the plot and any resulting inaccuracies are mine alone.
Thanks to Jane Wood and all at Quercus for their hard work on my behalf. Thanks, as ever, to Tif Loehnis, Rebecca Folland and all at Janklow and Nesbit. Love and thanks always to my husband Andrew and our children, Alex and Juliet.