Isaac Proctor was an agent and assassin for Moriarty. In his first appearance in "A Landmark Story", Sherlock texts Moriarty with Daniel Gottlieb's phone, arranging a meeting at diner. Waiting outside, Sherlock sees Issac waiting for the meeting. When Issac leaves Sherlock tails him, but is cut off by a train. Sherlock takes a series of photos, then goes home and edits them together, creating a picture of John Douglas. Sherlock arranges a meeting with Douglas, but he was assassinated by Isaac when he was about to reveal information about Irene Adler and why she had to die.