UFOs are the biggest mystery of our time and somebody-or something- seems determined to keep it that way. Thousands of UFO researchers and witnesses have told of terrifying encounters with mysterious men, usually dressed completely in black, who threaten terrible consequences if they don't keep silent. The Men in Black seem to appear out of nowhere, know facts the witnesses haven't divulged to anybody, and frequently display bizarre behavior, leading some to question whether they are in fact, human.