Shutter Island by Dennis Lehane.
"The year is 1954. U.S. Marshal Teddy Daniels and his new partner, Chuck Aule, have come to Shutter Island, home of Ashecliffe Hospital for the Criminally Insane, to investigate the disappearance of a patient. Multiple-murderess Rachel Solando is loose somewhere on this barren island, despite having been kept in a locked cell under constant surveillance. As a killer hurricane bears relentlessly down on them, a strange case takes on even darker, more sinister shades—with hints of radical experimentation, horrifying surgeries, and lethal countermoves made in the cause of a covert shadow war. No one is going to escape Shutter Island unscathed, because nothing at Ashecliffe Hospital is remotely what it seems." taken from Amazon.com
I picked this up because the movie is going to take forever to be available on my Netflix queue. It's a good story but not sure I liked the book. The writing style was a bit confusing & hard to follow since it wasn't from any one person's point of view.
Good for the story but the movie might be better