After their recent services to the Crown (The Catacomb Conspiracy), aging archaeologist Toby Glendower and anthropologist Penny Spring are en route to the rented Cape Cod home of their offspring for a much-needed rest. Chicken pox sends the kids and grandchildren back to city, but Toby and Penny remain to solve the mystifying murder of schoolteacher Clara Bacon, found propped up in her classroom surrounded by clues--each pointing to a prominent Cape resident. Ernie Birnie (The Cape Cod Caper, 1988) is now head of the Barnstable police and calls on the sixtysomething duo for help; they, in turn, lean on plucky mystery-writer Jocelyn, eager to try her hand at solving her first real murder. All are soon enmeshed in a convoluted scheme involving laundering stolen Canadian bullion by tipping it into the ocean and claiming it as sunken treasure. Cape fans will recognize the well-documented traffic snarls, but, otherwise, the local color is pretty thin here. Less sniping between Toby and Penny--a plus--and a better effort than usual from the fair-to-middling Arnold.