"Many dangers lurk in the deep-the worst of them are human. Thirty minutes into what should have been an easy, beginner-level dive in a remote Florida lake, the rim of a cave collapses, trapping two of Doc Ford's friends. Ford himself manages to escape and quickly surfaces to find help-but that's when his troubles only begin. Two men are waiting for him on the shore, and they are not the kind of men you want to meet at any time. Murderers and ex-cons,...