More Keel.
As I stated regarding "Strange Creatures From Time & Space," the same holds true for this book, which was published soon after-- For anyone unfamiliar with John Keel, this is a great introduction to the author. He does not merely present accounts of "strange creatures;" he provides analysis to elaborate his theories regarding things which modern science cannot easily explain. Whether or not one agrees with his ideas, he certainly provokes the readers to think for themselves and (hopefully) question their preconceived notions. If you enjoy these two works, you will probably want to progress to "Operation Trojan Horse" and "The Mothman Prophecies," where Keel further develops his worldview (actually, his universeview) of that which mankind regards as mysterious.