"Through a window at the top of the buildings, which gives on to the roof," I answered. "One of the bars to this window was wrenched out, and the roof outside shows that men have stood there to accomplish the work. The bank is not an isolated building. A journey from its roof to the roofs of the adjacent buildings is not difficult, and I am working on the hypothesis that the thieves entered the adjacent block of offices and crossed the roof. There are two facts which seem to support this idea. Quite recently some repairs to the roof of the building became necessary, and two men were engaged upon it for three days. They may have been members of the gang, and it is curious they have left the employment of the firm which had the work in hand. So far I have failed to trace them. Again, an office in this building, occupied by a man named Bowman, calling himself a mortgage broker, has remained closed since Saturday. Bowman has not been there very long, but until now has been regular in his attendance. I am inclined to think he will not be seen there again." "How much do these bags of gold weigh?" asked Zena thoughtfully. "They are very heavy," I answered. "But how was the gold got away?" said Zena. "I can only surmise as to that," I said with a smile. "The street which runs beside the bank is somewhat dimly lighted, and almost opposite to the private door of the bank there is an archway leading to a small yard and the premises of Thorne & Co., wine merchants. The archway is closed by a gate. The locked gate would present small difficulty to a gang which had carefully prepared their scheme, and very likely a motor car was driven under this archway ready to take the spoil away." "It is possible, but I should want to find out something more about Frederick Ewing," said Zena. "I am inclined to think that is a suggestion worth consideration," said Quarles. "This is a case in which one looks for negatives to a series of propositions. We may ask first, whether a gang, however expert, could have carried out such a robbery, knowing when and where to go and what to take, without some help from within. The answer seems to be, no. Was that information obtained merely through somebody's indiscretion? Hardly! Only a few people would be capable of giving the necessary information. Coulsdon, the porter, might give it. Did he? The fact that he was knocked insensible does not exonerate him; that might be part of a prearranged plan. On the whole, however, Ewing appears to be a more likely person. He was dishonest, that we know; he was in a position to give the information; he would be smarting under the disgrace of his dismissal; an offer of a substantial payment would, therefore, be tempting; and, moreover, he is not to be found."