'The Unspeakable Gentleman' is a novel written by John P. Marquand. The book follows the life of Captain Sheldon, a notorious scoundrel and former seafarer, who returns to his seaside home after years of living a life of debauchery and abandonment. With French Revolutionaries hot on his trail and a mysterious letter and young lady to protect, the Captain reveals to his son Henry and all those around him that he has lived a life of vice and disregard for society's values. But with danger lurking at every turn, will the Captain be able to keep himself and those in his care safe from harm?