Dumas came to write The Count of Monte Cristo not by design but chance. He was originally commissioned by a French publisher to write a series of articles on the history of Paris. But seeing the success of novels serialized in newspapers the publisher impressed on Dumas to change the commission into a novel which became The Count of Monte Cristo. Dumas being a voracious reader already had the germ of an idea which he got from police archivist Jacques Peuchet's Memoires Historiques.
The Diamond & The Vengeance (from Peuchet's memoirs) tells the story of one Francois Picaud who, in 1807 was denounced as an English spy by his friends before his impending marriage to a young woman named Marguerite. Behind Picaud's predicament was Mathieu Loupian who was jealous of his relationship with Marguerite, not unlike Fernand who was jealous of Dantes' relationship with Mercedes.
Picaud winds up under house arrest at the castle of Fenestrelle in the service of a wealthy Italian. Picaud became like a son to the man, who was abandoned by his family. So Picaud inherited his wealth, and the location to a treasure. Picaud secures the fortune, and using the identity of Joseph Lucher returns to Paris.
In Paris he finds out that Marguerite and Loupian are married; he also bribes his way to finding out information about those responsible for his sentence. Picaud stabs, burns, poisons, impersonates and prostitutes his way to vengeance, till he is killed by a co-conspirator who confessed everything on his deathbed.