Robert Hugh Benson 
Oddsfish! 

Oddsfish! (a title derived from King Charles‘ favorite epithet) is the last of Benson’s historical romances and describes the plots and political movements of the closing scenes of the life of Charles II. Interwoven with the accurately portrayed events and places of the time are fictitious characters, including the narrator, Mr. Roger Mallock and his cousin and lady-love Dolly. Sent by Pope Innocent XI to Charles‘ court as a diplomatic representative of the Vatican, Mallock becomes a trusted confidant of the King and acts upon Charles’s deathbed wish to give his confession to, and receive absolution from, a Catholic priest. (Goodreads)