“Yes.  For once our chemists had grasped how these tubes could be used, we knew what to look for when the workmen were searched on entering the factory.  Two days ago we caught a man.  He had one of these little tubes in his mouth and in the lining of his waistcoat, just a little high explosive, so little was necessary that it must escape notice unless you knew what to search for.  Yes, we caught him and he, the good fellow, the good honest neutral”—­it would be difficult to describe the bitterness and scorn which rang through Marnier’s words, “has been kind enough to tell me how he earned his German pay as well as his French wages.”

Hillyard leaned forward.

“Yes, tell me that!”

“On his way to the factory in the morning, he makes a call.”

“Yes.”

“The one on whom he calls fills the tube or has it just filled and gives it to the workman.  The time fuse is set for four hours and a half.  The workman has so arranged it that he will reach the factory half an hour after the tube is filled.  He passes the searcher.  At his place he takes off his waistcoat and hangs it up and in the pocket, just separated from the explosive by the lining of the waistcoat, he places, secretly, the tube.  The tube has now four hours of life and the workman three and a half hours of work.  When the whistle goes to knock off for luncheon, the workman leaves his waist coat still hanging up on the peg and goes out in the stream.  But half an hour afterwards, half-way through the hour of luncheon, the acid reaches the explosive.  There is a tiny explosion in that empty hall, not enough to make a great noise, but quite enough to start a big fire; and when the workmen return, the building is ablaze.  No lives are lost, but the factory is burnt down.”

Hillyard sat for a little while in thought.

“Perhaps you can tell me,” he said at length.  “I hear nothing from England or very little; and naturally.  Are we obtaining Spanish workmen, too, for our munition factories?”

“Yes.”

It was clear now why B45 was especially suitable for this work.  B45 was Mario Escobar, a Spaniard himself.

“And filling the tubes!  That is simple?”

“A child could do it,” answered Marnier.

“Thank you,” said Martin Hillyard.

The next evening he left Paris and travelling all night to Boulogne, reached London in the early afternoon of the following day.  Twenty months had passed since he had set foot there.

CHAPTER XIX

UNDER GREY SKIES AGAIN