Cannons, antique dealers visitors to England unusual wave discover body (in bore). Caught up in investigations

Dave Cannon, the American rare book and antique dealer, and his English wife come to the peaceful Gloucestershire village of Wade, to have a holiday and perhaps pick up a treasure or two. Cannon finds a treasure, all right -a small thirteenth century silver-gilt casket. But that rare medieval object ensnarls Cannon in a complicated plot involving the phenomenon on the river Severn of a tidal wave called the bore; a bizarre young poet; an ancient Gloucestershire family; and a very modern murder.