In the 1970s, Madeleine Blais's in-laws purchased a vacation house on Martha's Vineyard for the exorbitant sum of $80,000. A little more than two miles down a poorly marked one-lane dirt road, the house was better termed a shack--it had no electricity or modern plumbing, the roof leaked, and mice had invaded the walls. It was perfect. Sitting on Tisbury Great Pond--well-stocked with oysters and crab for foraged dinners--the house faced the ocean and...