Ever since humans were first able to think consciously about the world around them, they have tried to find out whether the concrete, rational universe we inhabit doesn't have something else behind it -- something revealed only in tantalizing glimpses. Unsolved Mysteries looks at some of these intriguing questions that humans have tried to grapple with, offering rational explanations where appropriate, but not ignoring the possibility of something that we cannot explain being responsible.An Eastern Airlines Lockheed Tri-Star crashed in the Everglades on December 29, 1972, killing the crew and most of the passengers. Undamaged parts salvaged from the wreck were subsequently incorporated into other aircraft under repair. Soon after, several people reported meeting the dead captain and flight engineer, either in the cabin or on the flight deck of some of these aircraft. It was as if the spirits of the two men were watching over other planes to ensure that a similar tragedy did not take place.