“I see,” admired Tignol.  “Well?”

“As it turned out, I didn’t find him, I haven’t seen him yet.  He was away on a trip when I got to Brussels, away on this trip that will bring him to Paris to-morrow, so I missed him and—­it’s just as well I did!”

“You got facts about him?”

“Yes, I got facts about him; not the kind of facts I expected to get, either.  I saw the place where he boards, this Adolph Groener.  In fact, I stopped there, and I talked to the woman who runs it, a sharp-eyed young widow with a smooth tongue; and I saw the place where he works; it’s a wood-carving shop, all right, and I talked to the men there—­two big strong fellows with jolly red faces, and—­well—­” he hesitated.

“Well?”

The detective crossed his arms and faced the old man with a grim, searching look.

“Papa Tignol,” he said impressively, “they all tell a simple, straight story.  His name is Adolf Groener, he does live in Brussels, he makes his living at wood carving, and the widow who runs the confounded boarding house knows all about this girl Alice.”

Tignol rubbed his nose reflectively.  “It was a long shot, anyway.”

“What would you have done?” questioned the other sharply.

“Why,” answered Tignol slowly, while his shrewd eyes twinkled, “I—­I’d have cussed a little and—­had a couple of drinks and—­come back to Paris.”

Coquenil sat silent frowning.  “I wasn’t much better.  After that first day I was ready to drop the thing, I admit it, only I went for a walk that night—­and there’s a lot in walking.  I wandered for hours through that nice little town of Brussels, in the crowd and then alone, and the more I thought the more I came back to the same idea, he can’t be a wood carver!”

“You couldn’t prove it, but you knew it,” chuckled the old man.

Coquenil nodded.  “So I kept on through the second day.  I saw more people and asked more questions, then I saw the same people again and tried to trip them up, but I didn’t get ahead an inch.  Groener was a wood carver, and he stayed a wood carver.”

“It began to look bad, eh?”

Coquenil stopped short and said earnestly:  “Papa Tignol, when this case is over and forgotten, when this man has gone where he belongs, and I know where that is”—­he brought his hand down sideways swiftly—­“I shall have the lesson of this Brussels search cut on a block of stone and set in my study wall.  Oh, I’ve learned the lesson before, but this drives it home, that the most important knowledge a detective can have is the knowledge he gets inside himself!”

Tignol had never seen M. Paul more deeply stirred. “Sacre matin!” he exclaimed.  “Then you did find something?”

“Ah, but I deserve no credit for it, I ought to have failed.  I weakened; I had my bag packed and was actually starting for Paris, convinced that Groener had nothing to do with the case.  Think of that!”