Mildred agreed and then began to plan excursions to this place and that, with the idea of making the stay of the visitors at Sheepeak pleasant. So agreeably did she behave and took such trouble in designing trips that Mrs. Bolstreath revised her opinion and began to believe that so nice a girl could not possibly know anything of Mrs. Jarsell's doings, whatever knowledge her uncle might be possessed of. And Dan, walking at top speed along the high road in a vain attempt to quieten his mind, was convinced that the inventor had some such knowledge. The idea which had brought him to his feet, and had sent him out to work off his excitement, was that the inventor was responsible for Mrs. Jarsell's presence in London at unexpected moments. She financed him and retained him at her elbow, so to speak, that she might utilize his capabilities and his clever inventions. If, on the day of the London to York race, Mrs. Jarsell was at the Peacock Hotel about the hour of nine o'clock--as she certainly was, on the evidence of Mrs. Pelgrin, who had no obvious reason to tell a lie--she could not have got to London by train or motor in time to murder Durwin. Yet she was assuredly at Blackheath, if the cinematograph was to be believed. Dan had hitherto been puzzled to reconcile apparent impossibilities, but at tea-time the solution of the problem had suddenly flashed into his mind. Mrs. Jarsell had travelled to town on an aeroplane. "It is about one hundred and sixty miles from this place to town," muttered Dan, walking very fast, and talking aloud to himself in his excitement, "so she could accomplish that distance with ease in three hours, considering that Vincent's machine can fly at sixty miles in sixty minutes. He said so and I proved that he spoke truly when I experimented with the machine he lent me. Mrs. Jarsell was at the Peacock Hotel at nine o'clock, and the cinematograph showed she was at Blackheath at one o'clock. The race started then, and Durwin was killed shortly afterwards. Sixty miles an hour means one hundred and eighty miles in three hours. Say she started at half-past nine--which she could easily do, leaving Mrs. Pelgrin immediately for Vincent's place--she could reach London by half-past twelve, if not earlier, seeing she had just one hundred and sixty miles to go. There would be no difficulty in her reaching Blackheath and stabbing Durwin at the time the death took place."