He stood for a moment in the disordered room, thinking. Under these new circumstances, what was his proper course?

First, it was obvious that he must make absolutely sure that this Mrs. Vane was really the woman he sought. Next, he must learn if she had really gone, and, if so, why, and, if possible, where. If her departure was a flight, he must find out how or by whom she had been warned. Lastly, he must follow her to her hiding-place and arrest her.

But he must not end with Mrs. Vane. Her husband must also be found. If she was Mrs. X, the receiver of the stolen diamonds, possibly the murderer of old Gething, Mr. Vane must be in it, too. It was inconceivable that he could have avoided becoming involved.

His first job must therefore be to make all the inquiries he could as to the mysterious occupants of Crewe Lodge. There were several obvious lines of research. First there was the house itself. People left the impress of their personalities on the houses they inhabited, and a careful search of this one must yield considerable information as to the pair. Next there were the servants. If they could be found, their testimony might prove invaluable. From the neighbours and local tradesmen and dealers he did not expect so much, but among them all some useful hints would surely be gleaned. Lastly, there were the house agents. They might or might not be able to help.

It was by this time nearly eleven, but he decided that his obvious duty was then and there to begin the search of the house, even if it meant an all-night job. He therefore called in Pye and Frankland, who were experienced in such work, leaving Constable Caldwell to patrol the grounds.

Then commenced an investigation of the most meticulous and thorough description. Taking the house room by room, the three men went over with the utmost care every piece of furniture, every book, every paper, every article of clothing. Hour after hour the search proceeded in spite of a growing weariness and hunger, and it was not until half-past six on the following morning that it was complete. Then in the growing daylight the three Yard men slipped out one by one on to the road, and joining forces round the corner, walked to the nearest tube station, and went to their several houses for breakfast. French rang up the Yard from the first exchange they came to, and arranged for a man to be sent to relieve Caldwell, who had been left in charge.

As French smoked his after-breakfast pipe before returning to the Yard, he jotted down in his notebook a list of the points which had struck him during the search. There was nothing that led him to either Mr. or Mrs. Vane, but there was a certain amount that was suggestive.

In the first place, it seemed evident that the departure of the lady had been sudden and unexpected. There was the evidence of the disordered bedrooms, of the used-looking sitting-room with the book evidently laid down where it could be picked up again without losing the place, of the ashes in the sitting-room fireplace and range, the used tea tray, and of the kitchen. There it appeared that cooking had been just about to begin, for a number of saucepans were on the range, and various kinds of food lay on the table as if ready for the saucepans. There was a good deal of food of various kinds about the kitchen and larder, and some wine and whisky in the dining-room sideboard. On the other hand, there was no evidence of any hurried departure on the part of the master of the house.

The date of the departure French thought he could roughly fix from the condition of the food. The milk, of which there was a bowl and two jugs, was sour, but not thick. Some fresh meat hanging in the larder was good. The bread was rather dry and hard. Some lettuces lying on a shelf in the scullery had gone limp. But some bunches of chrysanthemums standing in water in the sitting-room, were quite fresh.

On the whole, he thought the evidence pointed to a flight some four days earlier, and this view was supported by another piece of evidence on which he had come.