Who is Mr. Rankeillor and what connections does he have to David? How is David able to convince him who he (David) is? What information confirmed David's story?

Mr. Rankeillor is Ebenezer's lawyer at the beginning of the novel, he is a respected man in Queensferry. David sees him as his gate to the Shaws and goes straight to him once returning to the Lowlands. After a few tests, Rankeillor trusts David and listens to his whole story. He had since broken ties with Ebenezer because of news that David had been kidnapped. He helps David trick Ebenezer into admitting to the kidnapping so he can get his rightful share of the Shaws. He also gives David letters so he can try to help Alan get home and James get a fair trial.