This is one of the early books in the UFO field that is one of the best. Major Don Keyhoe was given an assignment by True magazine to investigate the cases of flying saucers that were being reported by so many people, including many pilots and other professionals. He thought they were either test rockets from us or the USSR. The book is how he investigated many cases that are now famous including the Captain Mantell case where he crashed.
He goes to the actual areas where these cases actually happened and interviewed the witnesses in the cases. He realizes he is dealing with something much different than he anticipated. The book may seem dated as Major Keyhoe has a chapter on space travel (and our limited knowledge on the effects of humans), but it is well worth the read. Major Keyhoe has a no nonsense approach to the subject, and that is different than many of the books out now. He slowly starts to realize that the flying saucers are not man made but from other worlds.
Many of the sightings dealt with actual nuts and bolts craft from up close. The pilots were given orders to chase them and even try to shoot them down.
I read the whole book when I started it as I could not put it down. This is one book that is recommend to all those who are interested in ufology. It is interesting to see how many outstanding cases there really are that the debunkers keep stating are not out there.
My only problem was the printing of the book. It has many typos in it and other small printing problems. I also did not like the little advertisement for the site at the bottom of many pages. Those are minor as the book itself is reprinted in its entirety and all the older names are used. One of the best UFO books out there.