“Not our natural enemies, doctor,” protested Mr. Singleton.  “We work for a conviction, of course, but we don’t throw obstacles in the way of the defence.  You know that perfectly well.”

“Of course I do, my dear sir,” replied Thorndyke, shaking the official by the hand.  “Haven’t I benefited by your help a score of times?  But I am greatly obliged all the same.  Good-bye.”

“Good-bye, doctor.  I wish you luck, though I fear you will find it ’no go’ this time.”

“We shall see,” replied Thorndyke, and with a friendly wave of the hand to the inspector he caught up the two cases and led the way out of the building.

CHAPTER IV

CONFIDENCES

During our walk home my friend was unusually thoughtful and silent, and his face bore a look of concentration under which I thought I could detect, in spite of his habitually impassive expression, a certain suppressed excitement of a not entirely unpleasurable kind.  I forbore, however, from making any remarks or asking questions, not only because I saw that he was preoccupied, but also because, from my knowledge of the man, I judged that he would consider it his duty to keep his own counsel and to make no unnecessary confidences even to me.

On our arrival at his chambers he immediately handed over the camera to Polton with a few curt directions as to the development of the plates, and, lunch being already prepared, we sat down at the table without delay.

We had proceeded with our meal in silence for some time when Thorndyke suddenly laid down his knife and fork and looked into my face with a smile of quiet amusement.

“It has just been borne in upon me, Jervis,” said he, “that you are the most companionable fellow in the world.  You have the heaven-sent gift of silence.”

“If silence is the test of companionability,” I answered, with a grin, “I think I can pay you a similar compliment in even more emphatic terms.”

He laughed cheerfully and rejoined—­

“You are pleased to be sarcastic, I observe; but I maintain my position.  The capacity to preserve an opportune silence is the rarest and most precious of social accomplishments.  Now, most men would have plied me with questions and babbled comments on my proceedings at Scotland Yard, whereas you have allowed me to sort out, without interruption, a mass of evidence while it is still fresh and impressive, to docket each item and stow it away in the pigeonholes of my brain.  By the way, I have made a ridiculous oversight.”

“What is that?” I asked.

“The ‘Thumbograph.’  I never ascertained whether the police have it or whether it is still in the possession of Mrs. Hornby.”

“Does it matter?” I inquired.