- Dr Watson: "Okay, what about his father? He wasn't one of your patients. Wasn't he some sort of conspiracy nutter-theorist?"
- Dr Mortimer: "You're only a nutter if you're wrong."
- Dr Watson: "And was he wrong?"
- Dr Mortimer: "I should think so."
- — "The Hounds of Baskerville"
Dr Louise Mortimer is Henry Knight's psychologist, who he hired to help him overcome the memory of the events of his father's death when he was just a child. On her advice Knight returns to the Baskerville area to try to piece together his memories.
She is seen through out the episode counselling Knight which seems to work, and helping him remember more details about the events of his father's death. Watson approaches her in order to gather information for the case but is ultimately derailed when Dr Frankland blows his cover.
Despite Watson having been revealed to having been lying to her in order to gain information, she still trust him and calls him when Henry has a mental break down and threatens her with a pistol before running off into the night.