John Dickson Carr 
Most Secret [EPUB ebook] 

Young Roderick Kinsmere was a country bumpkin when he strolled into the Great Court of Charles II’s Whitehall Palace. Three days later he had lost his fortune, gained a wife, fought for — and been outwitted by — his king, and no one would ever call Rowdy Kinsmere a bumpkin again. It was 1670 and London was a teeming, filthy, dangerous and splendiferous place. The king was in trouble and Roderick was surrounded by plots and counterplots. And somehow everything centred on the beautiful sapphire ring he had inherited from his father …’Mr Carr has contrived a fine, adventurous entertainment of politics and piracy, espionage and murder’ The Times