"By making a bold move," was the detective's reply. "The Germans were already bargaining for these negatives when I became convinced that the girl was only the tool of a man who had also been a photographer, and who had led a very adventurous life--an American living away in the country, near Colchester, under the name of Charles Sandford."
"Sandford!" I gasped, staring at him. "What is the girl like?"
"Here is her portrait," was the detective's reply.
Yes! It was the sweet face of my nightmare!
"What have you discovered regarding Sandford?" I asked presently, when I had related to the two men the story of the meeting at Salisbury and also my night's adventure.
"Though born in America and adopting an English name, his father was German, and we strongly suspect him of having, on several occasions, sold information to Germany. Yesterday, feeling quite certain of my ground, I went down into Essex with a search warrant and made an examination of the house. Upstairs I found a very complete photographic plant, and concealed beneath the floor-boards in the dining-room was a box containing these negatives, many of them being of your maps of the Clyde defences, which they were just about to dispose of. The man had got wind that we were keeping observation upon him, and had already fled. The gang consisted of an old hump-backed woman, who posed as his mother, a young woman, who he said was his married sister, but who was really the wife of his man-servant, and the girl Drew, who was his photographic assistant."
"Where's the girl? I suppose you don't intend to arrest her?"
"I think not. If you saw her perhaps you might induce her to tell you the truth. The plot to photograph those plans while you were insensible was certainly a cleverly contrived one, and it's equally certain that the two women you met in Salisbury only travelled with you in order to be convinced that you really carried the precious maps with you."
"Yes," I admitted, utterly amazed. "I was most cleverly trapped, but it is most fortunate that we were forewarned, and that our zealous friends across the water have been prevented from purchasing the detailed exposure of our most vulnerable points."
That afternoon, Gertie Drew, the neat-waisted girl with the fair face, walked timidly into my room, and together we sat for fully an hour, during which time she explained how the man Sandford had abstracted the portfolio from my car and substituted an almost exact replica, prior to sending Bennett back to Colchester, and how at the moment of my unconsciousness--as he was searching me for my key--she had entered the dining-room when I had opened my eyes, and staring at her had accused her of poisoning me. She knew she had been recognised, and that had caused her alarm in the "Carlton."