Thomas B. Costain 
Below the Salt [EPUB ebook] 

Richard O’Rawn had lived a long, full life. He had attained material success. He had served his country well in the United States Senate, loved and respected by his constituents and the rest of the nation. Now that his life was almost at an end, Senator O’Rawn had to share the mystery he had kept secret for so many years with someone else.
It was a mystery set in lusty Plantagenet England and revolving around Eleanor of Aquitaine, her granddaughter–the beautiful 'lost princess’–and the historic signing of the Magna Carta. Together with a young American writer, Richard O’Rawn would take his last journey back through the centuries–a journey rich with intrigue, romance, and adventure.