Georgette Heyer 
The Great Roxhythe [EPUB ebook] 

Lord Roxhythe is a patriot. He loves his king and his county . . . in that order with an undying passion. When faced with a mission for his king, King Charles, that many would quaver at accepting Roxhythe accepts without hesitation. While those around him question if what is good for Charles is indeed good for England Roxhythe does not. He is a royalist of a different age.
Masterfully written with cutting dialog and dazzling prose. Full intrigue, adventure, and rich details of the time and place. A must read for all Georgette Heyer fans.