In the Davinci code Robert Langdon has started investigating the murder and the mysterious message that the victim left behind. He receives a message from Sophie which is very helpful to him. Soon after he learns that he himself is a suspect because of his meeting with the victim that was cancelled. He also learns of a tracking device that was planted on him but he decides to keep it with him. Sophie also tells him that the message read, "P.S. Find Robert Langdon." but the police erased it before he got there. He then learns that the victim was Sophie's grandfather but they weren't very close. Though Langdon knows much about the victim he still does not have any leads on where to search to uncode the message. Sophie also believes that the "P.S." in the message means princess Sophie which is what her grandfather called Sophie until they had their falling out which has not been described in the book yet.