is not automatically alluring unless you appreciate the classic constraints of an Agatha Christie puzzle; in that case it's irresistible. Shutter Island can be reached only by ferry. The doors of the institution are either locked or watched. The book's main character, United States Marshal Teddy Daniels, has been sent to investigate the disappearance of a patient, a barefoot woman who vanished from a locked cell and left behind an encrypted message no one understands.