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