Sant of the Secret Service by William Le Queux

Back in Curzon Street, completely at a loss, I flung myself into a big arm-chair, and over a succession of pipes tried to piece our disconnected facts into a consecutive whole. Shackleton, or Schack, had moved from Newcastle to Bristol before the war, and I had little doubt that he had done so by express orders from the Koniggratzer-strasse. From this I argued mentally that Bristol would almost certainly be the seat of his main activities, and that his early return thither might be looked for with some degree of confidence. Added to this, we knew from the frank declaration of a high port official that the Bristol Channel towns were swarming with spies, and I felt little doubt that they were acting under Schack's direction. On the whole, now that we had apparently lost the two men in London, Bristol seemed the most promising base for our operations.

I decided therefore to return, and, leaving Madame at the Grosvenor in London, I took Aubert with me, together with an English secret agent whom I will call Moore.