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.
There was no sign whatever of activity within, or of any business about to be carried on. Thus, day followed day, Busch and Dubois spending most of their time within those high walls which held their secret.
One curious thing was the number of telegrams delivered there. Sometimes they sent and received as many as fourteen or fifteen in a day. How I longed to know with whom they were in such constant communication.
Suddenly, after the third day, the shoal of wires entirely ceased. Busch and Dubois, instead of going to the factory, spent the day in the country, taking train to Patrington and walking through Skeffling went out to Kilnsea, opposite Great Grimsby at the entrance to the Humber.