In some mysterious family feud or unintended slight, Jane Barlow Schwartz lost a friend, her cousin and soul mate Martha. But years later, surrounded by the exotic wildlife of the Galapagos, Jane and Martha meet again. There, amid the antics of blue-footed boobies and red-lipped batfish, Jane sets off on a quest through her family history to pinpoint the moment when Martha was no longer the Martha she knew. In the process, she ponders instinct, natural selection, and the oddities of evolution that transform us.