"Herrn Dr. H. Weiss," Thorndyke read aloud. "German stamp, postmark
apparently Darmstadt. You notice that the 'Herrn Dr.' is printed and the
rest written. What do you make of that?"

"I don't quite know. Do you think he is really a medical man?"

"Perhaps we had better finish our investigation, in case we are
disturbed, and discuss the bearings of the facts afterwards. The name of
the sender may be on the flap of the envelope. If it is not, I shall
pick the lock and take out the letter. Have you got a probe about you?"

"Yes; by force of habit I am still carrying my pocket case."

I took the little case from my pocket and extracting from it a jointed
probe of thickish silver wire, screwed the two halves together and
handed the completed instrument to Thorndyke; who passed the slender rod
through the grille and adroitly turned the letter over.

"Ha!" he exclaimed with deep satisfaction, as the light fell on the
reverse of the envelope, "we are saved from the necessity of theft--or
rather, unauthorized borrowing--'Johann Schnitzler, Darmstadt.' That is
all that we actually want. The German police can do the rest if
necessary."

He handed me back my probe, pocketed his lamp, released the catch of the
lock on the door, and turned away along the dark, musty-smelling hall.

"Do you happen to know the name of Johann Schnitzler?" he asked.

I replied that I had no recollection of ever having heard the name