The blackmail is achieved in this manner: Alan arrives at the Shaws house and poses as a man working with Captain Hoseason. He says that he has Davie in his care, and he's willing to kill Davie or to keep him a prisoner at Ebenezer's pleasure, as long as Alan gets some money out of it. By using this pose, Alan manages to extort a confession from Ebenezer that he sent Davie with Captain Hoseason to be sold to a plantation in the Carolinas. Once Ebenezer is tricked into admitting this, Mr. Rankeillor appears from a hiding place nearby and tells Ebenezer that, if Ebenezer doesn't want to wind up in jail for kidnapping, he'd better agree to Davie's demands for money. So Ebenezer folds, and Davie ends the book a rich man.