“‘If you wouldn’t mind,’ said Strike. ‘I’m particularly interested in the emergency patient who kept Margot late.’”1

Right before Margot was scheduled to leave on the night of 11 October 1974, an emergency patient came in with abdominal pain. According to the receptionist, Gloria, Margot agreed to see her before leaving that evening.2

Because Margot was late to meet Oonagh, she didn’t type up any notes on Theo’s visit.3 This, along with the fact that Dr. Brenner didn’t believe Theo looked feminine enough to be a woman, created an air of mystery surrounding Theo’s identity.4 The police put out an appeal for her to come forward, but she never did.5

1,2: Troubled Blood, Chapter 10
3: Troubled Blood, Chapter 13
4: Troubled Blood, Chapter 10
5: Troubled Blood, Chapter 13