"And who are you?"
"A friend," said the voice with a hollow, whispered laugh. "I, too, shall be somewhere in the inner room, where I can trap the enemy. I shall force him into your hands! Once you have captured him, you can search the house."
"I understand," said Cardona grimly. "When shall I enter with my men?"
"When you receive my signal, a shot fired from within the house. Then The Black Master will know of my presence; but he will be at my mercy."
The whole scheme sounded fanciful to Cardona; nevertheless, the impressiveness of that sibilant voice made him realize that this was not a hoax.
"I am counting on you," said the voice, "because this man is a mastermind. He must be captured, and his identity revealed — otherwise innocent men will go to their deaths. Do you understand?"
"Yes. Where is the house?"
The laughter that came over the wire was soft with mockery. It made Cardona realize the ingenuity of his informant. Without the location of the house, all these plans were useless.
"That," said the voice, "is something that you will learn only if you again promise to obey my instructions to the final detail.
"No matter what happens — no matter what you may suspect or see, you must not move or mention your plans until you receive my signal. Do you promise?"
"Yes," agreed Cardona with sincerity.
"Then take down this address."
Cardona scrawled the final data upon a sheet of paper. He had hardly finished when he heard the click of the receiver at the other end.
The detective pocketed the address that he had written, together with the diagram. When Joe Cardona agreed upon any plan, he adhered to it. He knew well who had uttered those mysterious words over the telephone.
The Shadow!
"Tonight!" muttered Joe Cardona. "Tonight!"
He smiled in anticipation. It was the kind of work that Joe Cardona liked. He had full authority to choose his men and go on any quest that he might choose. He thought of Inspector Burke's surprise tomorrow.
This talk of a Black Master was mysterious — but The Shadow was a man of mystery. He had guided Cardona in the past. Tonight, the detective knew, would reveal new and sensational results that might lead to a final solution of the crimes which had terrorized New York.
"Tonight!" repeated the detective. "Until then, I keep mum!"
CHAPTER XIX. ENTER THE SHADOW
THE telephone rang again beside Joe Cardona's desk. Doctor Zerndorff was on the line.
"I would like to see you," said the criminologist. "It is very important! I cannot tell you now!"
Cardona glanced at his watch. It was still early in the afternoon.
He rode uptown to Zerndorff's apartment. There, Doctor Zerndorff smiled pleasantly.
"All is well, Herr Detective," said Zerndorff. "Those men we have captured, they are guilty, yes? We have finished our work — and it is to you that all the credit belongs. Yes, to you!"
"I guess we've cleaned them up, professor," Cardona smiled. "Only—" He stopped abruptly. He seemed to hear the voice of The Shadow, with its warning words.
"You think there are others, yes?" questioned Zerndorff.
"Perhaps," said Cardona.
"How many?"
"There may be another man—"
"Impossible!" There was impatience in Zerndorff's declaration. "Impossible! We have captured them all!"
Cardona became silent. He remembered his agreement with The Shadow. Yet this positiveness of Zerndorff made him wonder.
He recalled the scene at the hideout of Killer Bryan, when Zerndorff's prompt shots had saved his life.
He glanced at the criminologist and noted that Zerndorff was eyeing him curiously.
"You have learned something, yes?" questioned Zerndorff, as though reading the detective's thoughts.
"What is it?"
"I can tell you better tomorrow, professor," replied Cardona. He was anxious to reveal his findings to Zerndorff; at the same time, he remembered The Shadow's instructions. He had guaranteed absolute secrecy.
He knew the devious ways of The Shadow. That strange man had an uncanny ability. If Cardona spoke now, he would be violating his agreement. Should The Shadow learn — well, Cardona realized that it might end the plans for tonight.
"Tomorrow, professor," said Cardona. "I can tell you better then. I have work to do tonight!"
"Tonight? But it is for tonight that I have called you here, yes. I have learned something that is very important!
"You remember those two men, Sforza and Pecherkin, that are now in the prison, yes? There will be a meeting of their friends, tonight, in a secret place! It is important that you should be there, in case that meeting should come to be!"
"How have you learned of this, professor?"
Doctor Zerndorff drew a folded paper from his pocket. He spread it before Cardona. It was inscribed with coded characters.
"This was sent me from Chicago," he explained, "by a government man. Today I have just discovered its meaning.
"It tells of the meeting, where these men will be. One of them is to come from Chicago; this was taken from him there, yes."
He wrote an address upon the margin of the paper, copying it from something he saw in the code.
Cardona recognized it as the location of Loo Link's Restaurant, a notorious den in the underworld.
He nodded. He knew of the back entrance, where gangsters came and went. Loo Link's had been raided, and was no longer under suspicion. An ideal place for men to congregate in secret, now that the police no longer watched it!
"There is only one thing," said Cardona, slowly. "I received a telephone call today, professor. I have promised to watch a certain house—" He drew the plan from his pocket.
"Here, I have been told, is the headquarters of a dangerous criminal. Someone — my informant, I believe — will be in this inner room, awaiting him. I am to wait outside with my men."
"A hoax!" exclaimed Doctor Zerndorff. "A hoax, yes! To lead you there so you will not be at the place I say! You must work with me, Herr Detective, that we shall find, perhaps, the evidence we shall need if these men shall receive a new trial—"
"I understand," replied Cardona grimly. He saw the plot now. He had believed the words which he had thought were from The Shadow — but here was Doctor Zerndorff, the mastermind of criminology, showing him his mistake.
"Do not go to that house!" advised Zerndorff. "Do not go today! Wait until tomorrow, yes! Do not believe these strange messages! They will mislead! You understand?"
Cardona nodded. He glanced at his watch. The afternoon was waning. He prepared to leave for headquarters.
"I cannot go with you tonight," declared Zerndorff, in a disappointed tone. "I wish that I might go with you. But you must do this by yourself, yes. I shall be busy here—" He waved his hand toward the laboratory.
Back at headquarters, late in the afternoon, Cardona received another telephone call. Once more, he recognized the voice which he had identified with The Shadow.
"You are ready for tonight?" came the voice.
"Yes," answered Cardona.
"You have kept your promise? You have told no one the location of the house?"
"I have told no one," replied Cardona truthfully.
The receiver clicked.
Darkness came, and the old house with the barred windows was completely shrouded and silent. Only long shadows of passing vehicles flitted along the side entrance that extended from the street. At last a long, thin shadow appeared beside the house.
Unlike the others, it remained. Finally it melted away, forming a blot against the side wall.
Shortly afterward, the loose grating of the black window moved in the darkness. It came free of its fastenings. The window sash opened; the grating went back into place as of its own accord.