ling a cypher?
Whither had this ragged messenger been going with the mysterious
package, and who had sent him, and why?

Guessing and musing, I reached home, and found that Hewitt had returned
before me. I made my way into his office, and came on him sitting at his
desk with a large lens, attentively examining a broken brass padlock.

"Am I bothering you?" I asked. "Are you on the bond robbery, now?"

Martin Hewitt nodded, with a jerk of the hand toward the padlock. "It's
a tough job," he said, "and I shall shut myself up presently and think
hard over it; just now I can't see my way into it at all. But what have
you got there?"

"Never mind," I said, "you're too busy now. I came across something very
odd at the hospital, which I thought would interest you--that's all."

"Very well, let me see it. I haven't begun my bout of cogitation yet.
Show me."

I put the envelope, the key and the paper on the table before him.
Hewitt, with a glance of surprise, picked up the key and examined it.
"That's curious," he said, and straightway began fitting the key to the
broken padlock on the desk.

"Why, man alive!" he cried, with a sudden burst of excitement, "where
did you get this? This--this is the article--the key--the very thing I
want!" He sprang to his feet and stared in my face in sheer amazement.
"Heavens, Brett, the thing's almost supernatural! I've a broken lever
padlock here, and of all things in the world I wanted to find the one
key that fitted it; and you calmly walk in and clap down the very thing
under my nose! Where did you get it?"

I told him the tale of the man who had been knocked down in Moorgate
Street, and I explained exactly how the paper, the key and the envelope
were found in relation to each other, and why I had brought them.

"And when was the man knocked over?" Hewitt asked.

"Some time between one and two o'clock, I should say," I replied. "They
brought him in well before two, at any rate."

Hewitt stared into vacancy for a moment, thinking hard. Then he said,
"Brett, I believe you've saved my reputation--not that it could have
suffered much, perhaps, in such a desperate case. But as a fact I had
already advised the calling in of the police, and should, perhaps, even
have given up the part of the case still left me. But this ought to put
me on the proper track. You see, every one of these patent lever locks
differs in some slight degree from all the rest, and only its own key
will fit it; a