“I mean that Zoe Havering was an actress before her marriage, that you and Japp only saw the housekeeper in a dark hall, a dim middle-aged figure in black with a faint subdued voice, and finally that neither you nor Japp, nor the local police whom the housekeeper fetched, ever saw Mrs. Middleton and her mistress at one and the same time. It was child’s play for that clever and daring woman. On the pretext of summoning her mistress, she runs upstairs, slips on a bright jumper and a hat with black curls attached which she jams down over the grey transformation. A few deft touches, and the makeup is removed, a slight dusting of rouge, and the brilliant Zoe Havering comes down with her clear ringing voice. Nobody looks particularly at the housekeeper. Why should they? There is nothing to connect her with the crime. She, too, has an alibi.”

“But the revolver that was found at Ealing? Mrs. Havering could not have placed it there?”