Fanks had enough to think about during that drive, the material being amply supplied by the woman who had so cleverly tricked him. What motive had brought this woman to Fellenger's chambers? For what reason had she taken her departure so suddenly? Was Emma Calvert dead? If so, who was the woman who bore so extraordinary a resemblance to her? If Emma Calvert were not dead, and this was she, why had she come to Half-Moon Street, and why had Robert fainted at the mere sight of her? All these questions presented themselves to the mind of the detective, and he found himself unable to answer any of them. If he discovered the mysterious woman there might be a chance of explanation; failing the woman, there remained the valet. But if the one was missing and the other was ignorant, Fanks knew not what he should do in so difficult a matter. As it was the height of the season, Piccadilly was crowded with vehicles of all descriptions, and the rate of progress was slow. Far, very far, ahead Fanks thought that he could descry the noticeable suncloth described by the constable, but of this he was not quite sure; therefore he remained in his cab instead of alighting to make certain. During a block caused by the congested state of the roadway it flashed into his mind that he had seen the woman's face before. He was doubtful if this was so, and yet he had an uneasy feeling that it was. The features of this unknown woman were familiar to him; but, as the Americans say, "he could not fix her nohow." It only remained for him to refresh his memory with a second glimpse; but at present he saw no chance of getting one. He despaired of finding the woman of whom he was in search. The hansom showed no signs of moving on, and, finding that he could walk quicker than he could drive, Fanks paid his cabman, jumped out, and raced along the crowded pavement. He saw a number of people whom he knew, but paying no attention to these he rushed along, intent on getting to his goal. At length his exertions were rewarded, for by the Isthmian Club he saw the wished-for cab ahead. It was turning into Berkeley Square, and, as the throng was thinner in the side street, Fanks secured another hansom with a likely-looking horse, and followed in its wake. It struck him that he might as well find out where the woman lived; therefore he did not attempt to catch up, but directed his driver to keep persistently on the trail. It was his only chance of gaining his ends with so crafty an opponent.