Wycliffe and the Dunes Mystery by W. J. Burley
Cochran Wilder disappeared fifteen years ago while on a coastal walking holiday in Cornwall. Recently released from a psychiatric hospital, he had been a serious embarrassment to his father, a prominent MP. Now his body has been found, buried in the dunes...Wycliffe suspects the involvement of six people, now well-established figures in the community, who at the time had been spending an illicit weekend at a chalet near where Wilder was found. All are disturbed by Wycliffe's interest and by a series of threatening anonymous communications. And then a second murder is committed...