It was not until nearly midnight that I was back at the hotel in Hull. Then, by judicious inquiry of the hall porter—who had become my particular friend—I ascertained that Gessner had left for London by the last train.
Should I follow, or should I remain in Hull?
I decided upon the latter course, and retired to bed, thoroughly fagged out.
Early next morning I went round to the telephone-exchange, rather than use the instrument in the hotel, and rang up Raymond.
To my delight he answered my call. He was at home.
I gave him a rapid digest of what I had discovered, and told him that the German had returned to Sydenham.
"All right, old chap," came his voice over the wire. "Vera will watch at this end, while you watch yours. If what I guess is right, they're doing something far more serious than surveying that flat coast north of the Humber. Be careful not to betray yourself."
"Trust me for that," I laughed. "Are you going back to Sheerness?"
"Yes. I'll be there all day to-day—and to-morrow I hope to get one of our friends the enemy arrested. That's what I'm trying for. Good-bye—and good luck," and he rang off.
Busch went to the factory where Dubois was already awaiting him. As I stood outside that building of mystery I wondered what devilment was being plotted within. It had not been cleaned or painted, the windows being still thick with soot, and several of them, which had been broken, were boarded up. The place had certainly not been cleaned down for years, and no wonder they had been suspicious of the stability of that chimney which towered so high towards the murky sky.