I have read every one of this author's books on these two characters and love the interaction between the two. Jon and David are two friends who became close during their military career, not only because of their humor and ribbing each other about their color (Jon is white, David black) but because of their talents of David being a brain at planning and strategy and Jon at military prowess and expertise. They are retired from the MANIACS, a military force composed of the U.S. armed forces of Marines, Army, Navy, Air Force, and Coast Guard, trained even more rigorously than even Delta Force and Navy Seals. Jon being the only surviving family member who inherited his grandfather's huge international company and vast fortune and David the owner of a great detective agency and investigative service based in Jon's main corporate headquarters, they were first drawn into treasure hunting and artifact recovery by accident but because of their training have become quite adept at what they do. The Secret Crown is book six and has brought the two together again for another adventure. While you can read each book individually I suggest going back and finding all the books and read them from the beginning. It is very interesting to see how the characters have evolved and how the writer has become even better with presenting the characters at their best. Only problem I have is having to wait so long between book releases. You can read the review about what this book is about but I wanted the review the author and characters and say to read them all. You will be glad you did.