“I suggest nothing,” said Poirot. “But I will remind you of this. Life was not very easy for that mother and daughter. There were bills⁠—there was constant trouble over small sums of money. Roger Ackroyd was a peculiar man over money matters. The girl might be at her wits’ end for a comparatively small sum. Figure to yourself then what happens. She has taken the money, she descends the little staircase. When she is halfway down she hears the chink of glass from the hall. She has not a doubt of what it is⁠—Parker coming to the study. At all costs she must not be found on the stairs⁠—Parker will not forget it, he will think it odd. If the money is missed, Parker is sure to remember having seen her come down those stairs. She has just time to rush down to the study door⁠—with her hand on the handle to show that she has just come out, when Parker appears in the doorway. She says the first thing that comes into her head, a repetition of Roger Ackroyd’s orders earlier in the evening, and then goes upstairs to her own room.”

“Yes, but later,” persisted the inspector, “she must have realized the vital importance of speaking the truth? Why, the whole case hinges on it!”