One day the old man did not go to the factory, but instead went forth upon one of his rambles. He took train from Hull to Hornsea, where the railway ends at the sea, and walked along the shore for several miles; indeed until he was three parts of the distance to Bridlington, when he suddenly halted near the little village of Barmston, and producing a neat pocket-camera took a long series of snap-shots of the flat coast, where I saw there were several places which would afford an easy landing for the invader.
The truth was in an instant plain. Old Busch was a "fixed-agent," who was carrying on the same work along the Yorkshire coast as his ingenious compatriots were doing in Norfolk, Suffolk, and Essex. The remainder of that day I kept a sharp eye upon him, and witnessed him making many notes and taking many photographs of the various farms and houses near the sea. He noted the number of haystacks in the farmyards--for his report on fodder stores, no doubt--and made certain notes regarding the houses, of great use, no doubt, when the Germans came to billet their troops.
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.
From the point where I watched I could see that the old man with considerable gesticulation was standing upon the shore facing seaward and explaining something to his companion.
The Belgian apparently put many questions to him, and had become intensely interested. Then presently his companion produced a paper from his pocket--evidently a plan, for he pointed out something upon it.
They both lit their pipes, and sitting down upon a rock discussed something quietly. Apparently Busch was making an elaborate explanation, now and then pointing with his finger seaward.
Where he pointed was the channel through which passed all the shipping into the Humber.
Then, after a time, he rose from where he sat, and seemed to be measuring a distance by taking paces, his companion walking at his side over the level expanse of sand.
Suddenly he halted, pointing to the ground.
Dubois examined the shore at that point with apparent curiosity. With what object I could not imagine.
They remained there for fully an hour, and the sun had already set when they returned to Patrington, and took the train back to Hull.
That old Busch was a spy I had proved long ago, but what part Dubois and Gessner were playing was not yet at all clear.
On the following evening, about ten o'clock, I saw Dubois near the Dock office, and on watching him, followed him to the factory, which he entered with his key. Beyond the gate was the small paved courtyard in which rose the high chimney. Within the factory he lit the gas, for I could see its reflection, though from the street I could not get sight of the lower windows.
The night was bright and moonlit, and as I waited I heard within the grinding of a windlass, and saw to my surprise, a thin light iron rod about six feet long and placed vertically rising slowly up the side of the chimney stack, evidently being drawn up to a pulley at its summit.
Dubois was hoisting it to the top, where at last it remained stationary, its ends just protruding beneath the coping and hardly visible.
Scarcely had this been done when Busch came along, and I had to exercise a quick movement to avoid detection. He was admitted by Dubois, and the door was closed and locked as usual.
I stood beneath the wall, trying to overhear their words. But I could understand nothing.
Suddenly a dull, crackling noise broke the silence of the night, as though the sound was dulled by a padded room.
Again I listened. Then at last the truth dawned upon me.
The spies had put in a secret installation of wireless telegraphy!
Those intermittent sounds were that of the Morse code. They were exchanging signals with some other persons.
Gessner was absent. No doubt the corresponding station was at that house high upon Sydenham Hill to the south of London, two hundred miles distant!
I waited for a quarter of an hour, listening to those secret signals.
Then I hurried to the telephone, and fortunately found Raymond at home.
I told him what I had discovered, and urged him to take a taxi at once down to Sydenham and ascertain whether they were receiving signals there.
This he promised to do, telling me he would 'phone me the result to the hotel at eight o'clock next morning.
Therefore I returned to the factory, and through the long night-hours listened to their secret experiments.
At eight next morning the telephone rang, and Ray briefly explained that Gessner, who had placed his apparatus upon the high flagstaff in his garden, had been receiving messages all night!
"Have you seen anything of Fowler?"
"No. But Hartmann has spent the night with Gessner, apparently watching his experiments. Couldn't you manage to watch your opportunity and get inside the factory somehow? I'll come north at noon, and we'll see what we can do."
At five o'clock he stepped from the London express, and together we walked down to the Imperial Hotel, to which I had suddenly changed my quarters, feeling that I had been too long in the close vicinity of the spy Dubois.
"It seems that they carry out their experiments at night," I explained.
"For in the daytime the wireless apparatus is no longer in position. I see now why they engaged a builder to examine the chimney--in order to place a pulley with a wire rope in position at the top!"
"But Gessner and Dubois are expert electricians, no doubt. Members of the Telegraphen-Abtheilung of the German army, most probably," remarked my friend.
"And who is Fowler?"
"A victim, I should say. He appears to be a most respectable man."
"In any financial difficulty?"
"Not that I can discover."
"But why have they established this secret communication between Hull and London?"