"I'm very sorry, dear, but I have that case to look into to-night," Jack said, with perfect truth. He saw that the hands of the big clock on the mantelpiece were creeping on to the hour. "Anstruther won't come up to-night; he said he should be here by eleven if he were. And he gave me a hint not to stay later. I shall see you at the Warings' to-morrow night. Good-night, darling."

Claire put up her red lips to be kissed. She would have seen Jack to the door, but he pointed out that the night was chilly and Claire's dress thin. Neither would he have the butler summoned. His coat and hat were in the hall, and he would get them himself. A moment or two later and he was standing in the garden behind the strip of shrubs. He was quite free to act now; he had nobody in the way. As he stood there, a distant church clock boomed the hour of eleven.

"Now we shall see what we shall see," Jack muttered. "I'm going to find whether there is a mystery of the house or whether these people are merely Anstruther's clients. Oh!"

As he spoke the dark curtain over the study window was pulled back, and the figure of the young man in the evening dress was clean cut against the light. Then a black arm pulled for the catch of the window, and the young man, pushing the blind aside, came out. He was wearing an overcoat now, and a tall hat. He seemed to be waiting for somebody.

Then the figure of the dark-faced, fair-haired girl came out. She was cloaked from head to foot in a blue wrap trimmed with feathers; her fair hair was not covered. No word was spoken, but Jack could see that they were conversing still by signs.

The watcher wondered if he had time to get inside the room. But that little idea was dismissed at the outset, for the young man pushed the window to carefully and the latch clicked. It was quite evident that the long sash closed with a spring lock, which was a most unusual thing for French windows to do. As the strange pair went down the side path Jack stepped into the open. He wanted to assure himself as to the window being fastened. He pulled at it hard, but it did not yield. At the same moment from the window of the room came a strange, brilliant crash of music. Yet that room was absolutely empty, as Jack would have been prepared to swear in any court of England.

"I'll wake up either from a dream or in a lunatic asylum presently," he muttered. "And now for those other people. Good thing they had no idea of being followed."

Jack was in the road now, and taking his way through the quiet nest of squares between Bloomsbury and Regent's Park. He could see his quarry a hundred yards or so before him; there was nobody else, and there was not the slightest chance of those in front being lost. A horse's hoof clicked on the wood pavement as a well-appointed hansom passed the tracker. Then he saw the hansom pull up by the curb and the deaf mutes in front jump in, as if the whole thing had been arranged, and drive off.

The thing was so sudden and unexpected that Jack was nonplused for a moment. There was no chance of following these people, for there probably was not another hansom within half-a-mile of the spot. Jack stood hesitating in the silence of the road; he could hear the steady flick-flack of the horse's hoofs as the rubber-tired hansom hurried on, and then suddenly the horse's hoofs stopped. They had not died out in the distance; they had merely stopped.

Jack hurried forward; he had not given up all hope yet. He might overtake the hansom and by good luck meet an empty one going towards the Strand. As he turned a corner, he saw to his surprise the figure of the young man in evening dress come silently towards him on the other side of the road. Then the stranger crossed the road and turned down the far side of the square as if he were going to complete the circuit and join his cab again. As the man vanished Jack heard a thudding sound, followed by a sound like the tearing of stiff paper, like the rattle of peas on a drum, a queer stifled cry, and then silence. On the impulse of the moment, Jack turned and followed.