Shutter island, by Dennis Lehane.

Shutter Island was enjoyable, but i thought I would like it better than I did. It had the right combination: set in an era with fedoras and spectacles; located on a remote island in an asylum; a great storm blowing in; deranged inmates roaming the grounds and trying to communicate crucial information in cryptic codes.
The problem.... I don't know if I had heard it at some point, but I guessed the ending within the first hour of the book. I almost never am able to do that.
Basically, without spoiling the ending (but you'll likely guess it as well), Shutter Island follows Teddy, some sort of special government operative, and his partner as they try to track down an inmate (excuse, me, Doctor - patient) who has gone missing. A surprise (or more likely not) awaits you at the end of their journey.

audio: 4.75 hours (abridged)
print: 385 pages