what unusual incident occurs at the local pub?

This happens in chapter 10. Pip goes to the Three Jolly Bargeman pub to bring Joe home. At the pub he spots a mysterious stranger with Mr. Wopsle and Joe. The stranger is all curious about Pip's relation to Joe. The creepy stranger pulls out a file and stars mixing his drink with it. The file happens to be the same one Pip stole from Joe’s smithy to give to the escaped convict. Before the man leaves he hands Pip two pounds mysteriously wrapped in a wad of cash!