The friendship between the Coleman and Shepherd families is as old and comfortable as the neighboring houses they occupy each summer on Cape Cod. Samuel and Sarah Coleman love those warm months by the water; the evenings spent on their porch, enjoying gin and tonics, good conversation and homemade clam chowder. Here they've watched their sons, Isaac and Asa, grow into fine young men, and watched, too, as Nate Shepherd, aching with grief at the...