One after another, members of the group either vanish or get killed before their bodies are found. After putting some clues together, Kit and Rob realize that everyone's earlier assumption is wrong; the kinsman of the deckhand injured when they arrived is a red herring. It also turns out that Muffy has a violently insane twin sister named Buffy, who has escaped. In fact, the "Muffy" they have been around since the first night was Buffy, pretending to be Muffy. They discover Muffy's severed head in the basement.