Shutter Island by Dennis Lehane

I love this book. I truly could not put it down. I felt it was very suspenseful and easy to follow. 
 In this story Teddy Daniels is a U.S. Marshall sent to Shutter Island to investigate the disappearance of a mental "patient". Shutter Island is used to house criminals that are mentally insane. He arrives on the island with his partner Chuck. They begin to wonder if there is even a patient missing, and start to hear rumors about the island's unorthodox drug experiments and brain surgery. Teddy soon realizes he doesn't know who to trust and soon fears for his life. 
This book takes many twists and turns that kept me guessing at each page.