If you're interested in UFOs and ETs, these are useful and important books, and it would be helpful to at least become familiar with the general contents and arguments by reading descriptions, editorial and reader reviews, and discussions on the Internet.
"UFOs: Generals, Pilots and Government Officials Go On the Record", by Leslie Kean. One of the best UFO books in recent years for the open minded general audience.
"UFOs and Nukes", by Robert Hastings, the world's leading authority on the subject (outside of the U.S.G.). It's pointless to speculate about the nature and purpose of the ET presence without understanding the information provided in this book, and other related sources of information about ETs and nuclear weapons.
"UFOs and Government: A Historical Inquiry", by Michael Swords and Robert Powell; and other contributors. This is a huge book, more like a college textbook than a typical popular UFO book--and someday it will certainly be studied by university students learning of this strange era of U.S. history (along with Richard Dolan's 'UFOs and the National Security State' books, et al.). It's rightly regarded by experts in the field as one of the most important UFO books in recent years, if not decades. For better or worse, it may be the last 'pre-Disclosure' book on the subject.
"Triangular UFOs: An Estimate of the Situation", By David Marler. See this post: If You're Interested in Contact, Read This Book: Triangular UFOs