In this case, the procedure was exactly the same.  The signal knock, the demand for a number, and the reply “Correct.”

Two knocks followed in quick succession on the door below.  The first man was quite unknown to Tommy, who put him down as a city clerk.  A quiet, intelligent-looking man, rather shabbily dressed.  The second was of the working classes, and his face was vaguely familiar to the young man.

Three minutes later came another, a man of commanding appearance, exquisitely dressed, and evidently well born.  His face, again, was not unknown to the watcher, though he could not for the moment put a name to it.

After his arrival there was a long wait.  In fact Tommy concluded that the gathering was now complete, and was just cautiously creeping out from his hiding-place, when another knock sent him scuttling back to cover.

This last-comer came up the stairs so quietly that he was almost abreast of Tommy before the young man had realized his presence.

He was a small man, very pale, with a gentle almost womanish air.  The angle of the cheek-bones hinted at his Slavonic ancestry, otherwise there was nothing to indicate his nationality.  As he passed the recess, he turned his head slowly.  The strange light eyes seemed to burn through the curtain; Tommy could hardly believe that the man did not know he was there and in spite of himself he shivered.  He was no more fanciful than the majority of young Englishmen, but he could not rid himself of the impression that some unusually potent force emanated from the man.  The creature reminded him of a venomous snake.

A moment later his impression was proved correct.  The new-comer knocked on the door as all had done, but his reception was very different.  The bearded man rose to his feet, and all the others followed suit.  The German came forward and shook hands.  His heels clicked together.

“We are honoured,” he said.  “We are greatly honoured.  I much feared that it would be impossible.”

The other answered in a low voice that had a kind of hiss in it: 

“There were difficulties.  It will not be possible again, I fear.  But one meeting is essential—­to define my policy.  I can do nothing without—­Mr. Brown.  He is here?”

The change in the German’s voice was audible as he replied with slight hesitation: 

“We have received a message.  It is impossible for him to be present in person.”  He stopped, giving a curious impression of having left the sentence unfinished.

A very slow smile overspread the face of the other.  He looked round at a circle of uneasy faces.

“Ah!  I understand.  I have read of his methods.  He works in the dark and trusts no one.  But, all the same, it is possible that he is among us now....”  He looked round him again, and again that expression of fear swept over the group.  Each man seemed eyeing his neighbour doubtfully.