Supernatural, book 3: Bone Key
Keith R. A. DeCandido2008

Sam and Dean are headed for Key West, Florida, home to Hemingway, hurricanes, and a whole lot of demons. The tropical town has so many ghouls on the loose that one of its main moneymakers has long been a series of ghost tours. But the tours are no more, not since one of the guides was found dead of an apparent heart attack... his face frozen in mid-scream. No one knows what horrors he saw, but the Winchester brothers are about to find out.

Soon they'll be face-to-face with the ghosts of the island's most infamous residents, demons with a hidden agenda, and a mysterious ancient power looking for revenge. It's up to Sam and Dean to save the citizens of Key West... before the beautiful island is reduced to nothing more than a pile of bones.