“Exactly,” agreed Kennedy.  “It is not a theory that confronts you.  It is a hard, cold fact.  I understand that perfectly.  What is, the address of this Albano’s?”

Luigi mentioned a number on Mulberry Street, and Kennedy made a note of it.

“It is a gambling saloon,” explained Luigi.  “Albano is a Neapolitan, a Camorrista, one of my countrymen of whom I am thoroughly ashamed, Professor Kennedy.”

“Do you think this Albano had anything to do with the letter?”

Luigi shrugged his shoulders.

Just then a big limousine was heard outside.  Luigi picked up a huge hamper that was placed in a corner of the room and, followed closely by Signer Gennaro, hurried down to it.  As the tenor left us he grasped our hands in each of his.

“I have an idea in my mind,” said Craig simply.  “I will try to think it out in detail to-night.  Where can I find you to-morrow?”

“Come to me at the opera-house in the afternoon, or if you want me sooner at Mr. Cesare’s residence.  Good night, and a thousand thanks to you, Professor Kennedy, and to you, also, Mr. Jameson.  I trust you absolutely because Luigi trusts you.”

We sat in the little dining-room until we heard the door of the limousine bang shut and the car shoot off with the rattle of the changing gears.

“One more question, Luigi,” said Craig as the door opened again.  “I have never been on that block in Mulberry Street where this Albano’s is.  Do you happen to know any of the shopkeepers on it or near it?”

“I have a cousin who has a drug-store on the corner below Albano’s, on the same side of the street.”

“Good!  Do you think he would let me use his store for a few minutes Saturday night—­of course without any risk to himself?”

“I think I could arrange it.”

“Very well.  Then to-morrow, say at nine in the morning, I will stop here, and we will all go over to see him.  Good night, Luigi, and many thanks for thinking of me in connection with this case.  I’ve enjoyed Signor Gennaro’s singing often enough at the opera to want to render him this service, and I’m only too glad to be able to be of service to all honest Italians; that is, if I succeed in carrying out a plan I have in mind.”

A little before nine the following day Kennedy and I dropped into Luigi’s again.  Kennedy was carrying a suitcase which he had taken over from his laboratory to our rooms the night before.  Luigi was waiting for us, and without losing a minute we sallied forth.

By means of the tortuous twists of streets in old Greenwich village we came out at last on Bleecker Street and began walking east amid the hurly-burly of races of lower New York.  We had not quite reached Mulberry Street when our attention was attracted by a large crowd on one of the busy corners, held back by a cordon of police who were endeavoring to keep the people moving with that burly good nature which the six-foot Irish policeman displays toward the five-foot burden-bearers of southern and eastern Europe who throng New York.