Not For Disclosure: The Truth about UFOs, the World's Best Kept Secret

by Jonathan Caplan

The most serious and sourced book ever published on the subject of UAPs (Unidentified Anomalous Phenomena), previously known as UFOs (Unidentified Flying Objects). Written by one of the UK’s most high-profile and well-respected barristers who has researched the issue for 50 years

For five decades, Jonathan Caplan KC (King’s Counsel) has been pulling together an extraordinary body of evidence about the existence of UAPs, and what he believes to be the world’s greatest ever cover up. Public perception of the UAP issue changed radically in July 2023 when David Grusch – a former Air Force intelligence officer – went public to US Congress under oath on live television that the United States was in possession of crashed non-human craft. His evidence ignited huge interest around the world. Pressure is mounting for the full story to be told, and Not For Disclosure is a landmark book on a subject that the public can no longer ignore.

In his quest for the full story, Caplan has travelled over the years to meet inside sources, including scientists, politicians, intelligence officers and ex special forces, in Washington, Israel and elsewhere. He has collated a vast amount of material from those in official positions who have trusted him and who have been prepared to talk confidentially about the subject. Over the last fifty years he has met and befriended most of the key individuals. His book is a detailed, up to date and in many ways shocking account of this fundamental and disturbing subject. It pulls together the strands of the phenomenon. It raises the debate.

The book includes significant new material including information about JFK and also about secret meetings held by President Truman and Secretary Forrestal. There will also be important and previously unpublished documents from the ‘Majestic 12’ group as well as striking new photos.

Genres: Nonfiction

272 pages, Kindle Edition

Published June 11, 2026

Reviews

[Raakel · Rating 5 out of 5]

No other nonfiction book has blown my mind like this. I have no opinion about UFOs and I am very skeptical of the whole subject but after reading this book I don’t know what to think. The author uses credible sources and provides compelling evidence. This is either the biggest hoax ever or the most life- and universe-altering information ever. I highly recommend this book to any curious person looking to dramatically challenge their worldview, even if they have no special interest in or belief about UFOs.

[Caleb · Rating 4 out of 5]

Caplan here provides a thoroughly researched and open-eyed summary and assessment of the situation, bringing together the very latest open source intelligence and historical data. He does not shy away the most bizarre facts, instead recounting all that can be credibly sourced, even if it strains our mainstream imagination. The book reads very quickly, and as of 2026 would be the perfect primer for someone interested in seriously engaging with this topic for the first time. After listening to the audiobook, which Caplan compellingly reads himself, I promptly bought it as a Father’s Day gift and hope it generates some good discussion. I especially appreciate the thorough mention of John Keel’s book ‘Operation Trojan Horse’ which I think best explains the true nature of “The Phenomenon”.

I will also add that I grew up as an American non-denominational Protestant Christian and engaging with this topic since 2021 has seriously challenged my faith. In large part thanks to my brother and the book/podcast “Lord of Spirits” I have realized that American Christianity and resulting atheistic scientism have major blind spots when it comes to NHI. I am now quite seriously investigating Eastern Orthodox Christianity, which maintains historical understandings of the unseen and which I think any disciplined investigation of the Phenomenon must contend with.

[M · Rating 4 out of 5]

A book heavily leaning on real life case studies based on individual testimonies and intense, decades long research. It reads well; alternating between descriptive scene setting details about UAPs and analytical comments. Great book if you want to challenge your personal perspective on UAPs and the classified world of alien sightings.

Overall, easy to read and very insightful.

[Del Khan · Rating 2 out of 5]

I purchased this book based on the early overwelming positive ratings. Mistake. This book has nothing new to add to the understanding of this complex phenomenon, and certainly the author is biased at the outset. Disappointed.

[paspatel · Rating 2 out of 5]

For a book that purports itself as approaching the topic with the eyes of a sharp lawyer seeking the truth, there is extremely little in this book to support any of the “facts” presented. At the very beginning of the book the author excuses himself for not providing sources for all parts of the book, arguing lots of information was provided on an anonymous basis — that’s fine as it is a reasonable argument, but then the book proceeds with zero citations whatsoever. No footnotes. Very little in terms of document sourcing. Barely anything.

If you can overcome this initial shortcoming, you must be ready to stomach a whole lot of storytelling with very little critical analysis. Most sources are taken as truthful because “why would they lie if they had nothing to gain from it?” or “there’s no reason to believe they’re not sound of mind.” Then the book dabbles into fringe stories, including categorically stating that several sources corroborate the existence of different alien races, including “Nordic-looking” tall ones (a story taken directly from nazi-leaning publications in the US from the 1950s). It is downhill from there.

The only somewhat interesting argument presented are the instances of odd phenomena seen by pilots, and military presence seen in locations where strange things reportedly happened. But this is merely curious and completely inconclusive, especially with the lack of quality in the “analysis” presented in the book.

The main theory presented here is that aliens have increased the frequency of their travels to our reality after the atomic bombs fell over Japan during WWII; since then they’ve been observing us more avidly, either with good or malicious intentions depending on the source you’re consulting. There is a lot of unexplained myth creation in this theory, and throughout the entire book.

Overall, it’s an entertaining read if you read it as speculative fiction or conspiracy literature. Also a must read for fiction authors exploring the alien theme. However, this is not a serious book

[Richard West · Rating 5 out of 5]

Once again, I'm sitting here with a book I purchased which Goodreads says won't be published for a few months yet. That's what happens when you purchase a British-authored book from a British bookseller. If Amazon doesn't have it, it hasn't been published! Sigh.

Kind of short at 251 pages this is an up-to-date look at what's going on in our skies, complete with speculation about who is flying these mysterious craft through the world's airspace. As might be expected, there's a short re-hash of older UFO (I still call them that even the correct term these days is UAP) sightings to set the stage for the more recent sightings.

Unlike many people who write these types of books, there's no "they're definitely from wherever" with the author letting the reader make the decision as to what and where these strange craft and the beings which are sometimes seen are and where they come from. This alone, adds a ton of credibility to the information.

If you've read other material on the subject, this might be a repeat of what you've read before, but that obviously can't be helped. If you're someone who is just curious as to what's going on - c'mon we've all seen that Tic Tac video 10,000 times - this is a good primer and introduction to the subject and is worthwhile reading.

I don't know about anyone else, but I'm with Fox Mulder on the old "X-Files" TV series - I want to believe!

[Bill Gibson · Rating 5 out of 5]

Up to date, extremely well researched and detailed as one would expect from a K.C. Has combined all the stories of the past that have had merit and offered proof of source and believability The reference section is a goldmine for those looking for their own authentication of his sources and an eye opener to some of the skeptics. There seems no doubt that the major world govts have known about the phenomena for years but the more I read it , the more I understood the reason for non disclosure

[Martin Sykala · Rating 5 out of 5]

Interesting book. I bought this on the strength that the author is a kc - has more credibility. While he demonstrates that we are definitely not alone, what is scary is perhaps what the uaps are planning? Some are not friendly. America it seems has more information and has only just released more material. Much of it from credible sources.

This book has lead me to purchase other titles from 'respectable' authors. What does the UK, china, Russia know? Only time will tell

[Austin · Rating 4 out of 5]

For the non-human-intelligence-curious among us, this is a very stimulating read! It gets better as it goes — the beginning feels like a hodgepodge of scattered anecdotal stories, but the chapter structure and theses evolve as the book progresses. I zoomed through the second half. The writing style was a bit lacking at times, but overall this is a great read and extremely thought-provoking. The truth is out there!

[Harrison · Rating 5 out of 5]

Readable, fairly comprehensive for its length, insightful. By far the best general UFO book, especially from a mainstream publisher, on the market today. Caplan did a wonderful job.

[Sean · Rating 3 out of 5]

A lot of interesting facts in his book, but also a bit too many conspiracy theories in the book.

[Adam · Rating 4 out of 5]

I wouldn’t say I am fully convinced but there are a lots of things that are presented in ways that make me question ‘surely not’ and then it appears to be true.
Wild stuff.

[Ben G · Rating 4 out of 5]

Bought on Kindle after looking for the 'Dyfed Enigma' that I was hoping too was on Kindle but sadly not.

Recently published and by a KC no less so also hoping that this will really kick the tyres on the 'evidence'. Let's see.

A robust overview of the (mostly) U.S government led projects designed to verify the existence and nature of UAP (unidentified arieal phenomena). I do hope he will follow this book up with another, examining British sightings, especially those in South Wales (e.g. Broadhaven (1970's) and Pentyrch (c.2010)) where the number of witnesses in both cases supports the existence of UAP in my opinion).