The dark stone changes those that possess it. Just after his eighteenth birthday, Sam finds a strange rock half-buried near some old abandoned train tracks. They were a normal suburban family. When Sam brings the stone home with him, things slowly unravel. His mother finds herself in situations she never imagined. His sister tries to resist her new impulses. Even Sam's married neighbor falls under the stone's spell.
When Pamela suspects that her twins have been being intimate with each other she tries not to overreact. Mentally that is, physically her reaction is barely controlled and far from maternal