Few women in the world could so perfectly adapt themselves to the ever-changing demands of the Secret Service as Madame Soyez. In her present circumstances she was absolutely at home, for she had been educated in part at a convent near Gembloux, and could assume the Belgian accent to perfection. It was an easy matter, therefore, for her to pass for what she pretended to be. In Hereford Road the Frenchwoman had established herself on my instruction for the purpose of keeping a watchful eye upon the quiet, long-haired, half-blind violinist, who, to all appearances, was eking out only a meagre existence, and whose clothes were of that shabby-genteel brand which usually betrays respectable poverty. But we knew enough of Heinrich's affairs to be convinced that the shabby-genteel role was deliberately assumed for purposes of deception. A splendid musician and a born teacher, Heinrich could command his own terms, and, as a matter of fact, he made a good deal of money. More than this, he was well known in high circles of Society, where his teaching abilities gave him the _entree_ to a large number of the best houses. And, of course, no one ever suspected that the half-blind old fiddler, crawling from house to house in the aristocratic quarters in which he found most of his pupils, was in reality the alert and dangerous agent of the enemy which subsequent events revealed him to be. CHAPTER ELEVEN. AN AIR RAID ON LONDON. One night of brilliant moonlight, I had just come in from a visit to a theatre and was glancing through the evening papers before turning in, when my telephone bell rang. On replying, I found the caller was Madame Gabrielle, and in consequence of the cryptic message she gave me I abandoned the idea of going to bed and remained keenly on the alert. For a full hour nothing occurred. Then I heard the air raid warnings for which I had been waiting and soon after the guns, distant at first, but gradually drawing nearer, began to boom out their defiance of the aerial invaders. For nearly two hours the raid continued at brief intervals, as squadron after squadron of Gothas came hurtling through the night sky on their mission of hate. As soon as the "All clear" signal was given, I hurried out and made my way rapidly to Harrington Street, a quiet thoroughfare at the back of Cadogan Square, with dark, old-fashioned houses, each with the deep basement and flight of steps to the front door so characteristic of a period of architecture which we may hope has passed away for ever.