"Something of the sort happened, for Lola went to Lady Eileen, and we were able to lay hands on her. But we failed to get her identified as the veiled woman who had visited the house in Grosvenor Gardens. I will confess that, at that time, I never had any suspicion that she was the actual murderess. We had no adequate excuse for detaining her after she handed the jewels over, with an explanation endorsed by Lady Eileen Meredith. I had taken her finger-prints, and they did not agree. "It was palpable that the attempt to baffle us was being shrewdly organised. I tried a different way of getting information--an attack, so to speak, by the back door. I enlisted the help of a criminal. He was acting more or less blindly, but by his help we stopped the burglary affair that was planned. In the pocket of one of the men we arrested, we discovered two advertisements, worded so as to convey a cipher key without exciting suspicion. We had them inserted, and naturally arranged to keep an eye on the office--for the word to-morrow suggested one to be inserted the following day. "There is always wisdom in gaining the confidence of those concerned in a case if you can. I was trying hard to establish friendly relations with Lady Eileen and Sir Ralph Fairfield. Each was difficult to handle, but with Sir Ralph I succeeded to some extent. I used him to try and learn something from her. She realised that the cipher was known, and went to the newspaper office to try and stop the insertion of the advertisement that might enable us to find Grell. Of course she failed, and we got a message which had been handed in by Petrovska. One of our men followed her. "We deciphered the message, and it enabled us to discover your hiding-place on the river. But the business was muddled, and you got away. We found the sheath of the knife used in the murder among other belongings you left behind. By the way, we understand that that dagger had belonged to Harry Goldenburg--how came it to be lying about your room?" Grell shook his head. "That is a mistake. The dagger was mine. It is possible that he had a similar one." "Yes, that is possible. But in the event, the point does not matter much. What was more important was, that we had driven you out of a secure hiding-place. "Meanwhile, Pinkerton's had been hard at work on the other side of the Atlantic, and many episodes of your private life were minutely examined. Their detectives it was, too, who had discovered that Goldenburg and Petrovska had in some way been associated with you. What they found out pointed to blackmail. Here appeared an adequate motive for you to murder Goldenburg." Grell tapped impatiently on the table, but did not interrupt. Heldon Foyle went on.