Project Blue Book and the investigation into UFOs closes. There is no evidence that mysterious objects represent any threat to U.S. national security. But harrowing incidents of UFO sightings continue and the unexplained malfunction of U.S. nuclear missiles after an incursion leave the U.S. defenseless. Three former Air Force officers, who served at nuclear weapons bases in the late 1960s, break two decades of silence to tell their story.