"Perhaps not," said Quarles. "Let us get back to the contents of this envelope. The driver would have us believe that the first taxi came direct from Richmond to Hyde Park Corner. We have strong reasons for believing it did not. Therefore, either he went out of his way, by Lady Tavener's orders, to call for some one, or some one got into the taxi without his knowledge. I sat on the driver's seat, Wigan, and I admit that, if fully occupied with driving, as he would be on a foggy night, entrance might have been made without his knowledge, but on one condition. The door must have been easy to open. The door of that taxi isn't easy. I tried it. It is exceedingly stiff, difficult to open, and impossible to close without a very considerable noise. Therefore Wood knows that some one entered, and we know that that some one must have walked on a road covered with brick dust and coal dust." "Who is it?" I asked. "Wood himself. He turned into the road we turned into. If Lady Tavener noticed that he had done so, she would not think anything of it. She would imagine the road was up and a detour necessary. As a matter of fact, she would not have time to think much, and I do not think she was alarmed, not even when Wood opened the door. As he did so I imagine he said something of this sort: 'I think it only right to warn your Ladyship that Sir John is suspicious.' He had to give some excuse for stopping the taxi and going to his fare. Whether he knew that Sir John was suspicious or not is immaterial. He had constantly driven Lady Tavener, and was probably aware that some of her friends were not her husband's. At any rate, some remark of this kind would allay her suspicions, and then--" "He murdered her?" asked Zena sharply. "Well, I fancy this is where we come to the question of suicide," said Quarles. "He intended to murder her, had his fingers on her throat, in fact, but the sudden excitement saved him. I think she actually died of shock, as the doctors declare. I think he was able to say something to her which caused that shock." "I can hardly believe--" "Wait, Wigan," the professor said, interrupting me. "You will agree that, from the first, Wood's evidence would naturally accuse Sir John. When you saw him and pressed him with the two questions I suggested he still sought to leave the impression upon you that Sir John was guilty; but since your questions showed there was a doubt in your mind, he admitted, to safeguard himself, the possibility of some one having entered the taxi surreptitiously. One other point which counts, I think. One of the lamps of the taxi, and only one of them, had recently been removed from its socket. I imagine he took it to make quite sure that Lady Tavener was dead." "But he had often driven Lady Tavener. Why had he waited so long?" said Zena. "And what reason had he for the murder?" I asked.