It's Halloween up in here. Edmond is getting the hang of identity swapping, and he now disguises himself as an agent from Thomas and French, an English investment firm, of course.
Edmond pays a visit to the Marseilles mayor, who he has heard has invested in a big part of Morrel's shipping business. But the mayor tells him to go see the inspector of prisons who has an even bigger share.
The inspector of prisons? How convenient! Edmond-disguised-as-an-investment-dude meets up with the inspector and buys out his share of Morrel's business. Then Edmond sneakily asks to see the prison records, explaining that Abbé Faria was his teacher once upon a time.
While scanning the prison records, Edmond looks up his own record and steals the incriminating letter that Fernand and Danglers forged so many years before. He also notices that Villefort indeed sentenced him to life-in-prison (he didn't really get a trial, and he never really got to find out what his prison sentence was).