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.
The sash was lowered. Silently, invisibly, as darkly as the night itself, The Shadow had entered the house of mystery!
This time there was no telltale spot of light within the house. The man who had come from the dark moved with certainty.
He found the door to the room with the hanging curtains. He unlocked it noiselessly, with the chosen key.
He passed silently through the dark room and found the opening in the curtains with unerring precision.
Then he passed through the smaller room. The curtains that hung over the alcoved window moved but made no noise. The Shadow was at his post, awaiting The Black Master!
Minutes went by; then hours. The little room was as silent as a tomb. Far away, from the front of the house, came a slight noise.
It was inaudible to those passing by in the street. Ordinary ears would not have heard it. But the keen hearing of the man in the curtained alcove was keyed to its highest pitch.
That noise was the opening of the outer door. It signified the arrival of The Black Master!
Silence followed.
A man had entered, but he, too, could move noiselessly through that strange house. There was no indication where he might be.
The man behind the shielding curtains was calm; in one hand he held an automatic, in the other a flashlight. He was waiting for the all-important moment - and he had not long to wait. His patience was rewarded by a slight sound in the inner room.
A small light clicked. The curtains of the alcove parted the fraction of an inch. Keen, invisible eyes peered through.
Still The Shadow waited. There was no need for haste. His presence was unknown. He knew that the men Cardona had promised would be ready for the signal. His finger was on the trigger of his automatic.
He was timing his surprise for the moment when The Black Master would appear.
At present, the enemy was somewhere in the room - not yet in sight of the narrow aperture between the curtains.
There was another purpose that governed The Shadow's actions. He was waiting to view The Black Master. Cold, calm, and calculating, he always studied his foe when the opportunity presented itself.
Here, tonight, The Shadow had invaded his enemy's lair by stealth. He had turned everything to his own advantage. He knew every spot on the floor of the house. He had made sure, the night before, that the alcove where he now waited was a safe point of vantage.
The fate of The Black Master rested in his hands, and he had decided that the master criminal should answer for his fierce campaign of unrestrained slaughter.
Never before had The Shadow encountered a foe so worthy of his prowess. Until this all-important moment, The Black Master had checked The Shadow at every turn.
The supermind of evil had surrounded himself with a veil of mystery that had thwarted The Shadow for many weeks. But now the end was at hand. The muzzle of the automatic moved between the curtains.
Blackened, the opening of the gun was totally invisible.
There was a noise in the room. Someone was moving closer to the curtains. An arm appeared across the room, near the table against the wall. Then came a body - that of a tall, stoop-shouldered man whose garments
