that it is a hoax until he reaches Albany.'
'But the note on the door -'
'That comes now.'
Zubian stole from the room and removed the piece of paper that Crayle had attached. He came back into the office and showed the scrawl to Carleton.
'Will return to-morrow,' read Carleton.
'Quite ingenious,' laughed Zubian. 'That note will do, no matter how long Crayle is away. One can read that message any day—because to-morrow is always in the future. However, it does not suit our purpose.'
Zubian carefully erased the word 'to-morrow,' leaving no trace of the writing. Instead, he inserted markings of his own. The altered note read:
Will return at 2.30.
Zubian crossed the hall and carefully replaced the note upon the door. He returned to Carleton, and offered new words of encouragement and explanation.
'Crayle never locks the office door,' he said. 'All the curios are in a safe. Visitors, if they find him absent, go inside and wait for his return. That is, such customers who know his ways.'
Reaching to the floor, Zubian pressed a button at the end of the green wire. This was a signal. Zubian arose and placed his hand upon the knob of the door.
'That means to cut off the water pipe,' he explained. 'Now comes my job— after that, we wait.'
Zubian crossed the hall, entered Crayle's office, and returned a few minutes later.
'All ready,' he remarked.
TIME dragged by slowly for Douglas Carleton, but Felix Zubian gave no signs of impatience. The international crook brought out two revolvers, and handed one to Carleton.
'There are other gunners up the hall,' he said, 'and they will come if I give an extra signal after the next one. He may try to escape— but he will be nearly helpless when he does.'
In the office at the end of the hall, on the same side as Hawthorne Crayle's curio place, another group of men were waiting. Beside them rested a metal tank, with a tube of rubber hose that lay coiled upon the floor. Squint Freston was in charge of his chosen gangsters. Strict silence ruled.
Two o'clock came. Back in their hiding place, Zubian and Carleton were tense.
Three minutes after the hour, a foot-fall sounded in the hall. Their eyes pressed to peekholes, the watchful villains recognized the form of Arnaud.
The visitor paused at the door of Crayle's office. He lifted the sheet of paper that bore the note. He opened Crayle's door and saw that the office was empty. He entered, reading the note. The door closed behind him.
'Now,' whispered Zubian, 'we are ready.'
He pressed the button to give the signal for action. Minutes ticked by while he and Carleton waited.
WITHIN Crayle's office, Henry Arnaud was seated in a chair, staring at the note, which he had plucked from the door. Such notes were common with Hawthorne Crayle. To be back at two thirty was one of the old man's favorite habits. Evidently he had forgotten his appointment with Henry Arnaud.
But now the sharp eyes of the waiting man studied the note. Henry Arnaud rested a long finger upon the marks that Felix Zubian had made.
Arnaud noticed a certain fact. Upon another sheet of paper, he wrote two phrases, one above the other: Will be back at 2.30.
Will be back at 2:30.
To an ordinary observer, the statements would have appeared the same. To Henry Arnaud, the one point of difference was obvious. In the first, the figure 2 was followed by a period; in the second, it was followed by a colon.
The upper statement corresponded with the one that Arnaud had found on the door; but the lower was the form that Hawthorne Crayle habitually wrote when he attached a message to the door. The old man was a creature of habit. It was not likely that he should change a style that he had used for years.
One dot alone made a colon differ from a period; yet the absence of that note was proof to Henry Arnaud that Hawthorne Crayle had not marked the figures '2.30' upon the message!
There was further proof as Arnaud held the paper to the light and rubbed his sensitive finger tip along it.
The original marking had been erased—this had been placed there in its stead!
Arnaud's soft laugh was inaudible outside the office. With wary, silent tread, the calm-faced man moved about the room. Not a single detail escaped his attention. Within two minutes he had inspected every spot. He stopped at a washbasin that was provided with a single faucet.
Carefully, Arnaud turned the handle of the faucet back and forth. He observed that it had been turned on; yet no water was issuing forth.
Arnaud drew a deep breath through his nostrils; he detected a very slight odor. He drew a match from his pocket and held it beneath the open faucet. The match went out.
Henry Arnaud smiled inscrutably. He knew the game now.
Through that pipe was coming—not water—but a noninflammable poison gas!
This room was a death trap. Within ten or fifteen minutes, should Arnaud be content to remain inactive, the office would be flooded with the death vapor, and its occupant would be overpowered.
Deliberately, Arnaud turned the handle to shut off the flow of gas from the faucet. He crept to the door, and drew an automatic from beneath his coat. Reaching upward, he placed his hand upon the knob as he crouched there, waiting.
IN the office at the end of the hall, Squint Freston was giving orders to his men. The metal tank was now in use. Its hose was attached to the spigot above the washbasin in that office.
The whole row of offices were on a single pipeline. That was the basis of Felix Zubian's scheme. With the water turned off, the pipe became the conductor of the murderous gas!
The handle of the metal tank was turned an full. Gas was surging through the waterline, restrained only by the fact that the building pipe could not accommodate the full flow. There was heavy pressure here—pressure sufficiently relieved when the faucet was open in Crayle's office.
But now, unknown to Squint and his men, the other end was plugged. There could be but one consequence. The pressure from the tank must be relieved. A break was sure to occur.
Like all breaks, it was due to take place at the weakest point. That was the connection between the tank and the water spigot in the room where the gangsters waited.
The break came with a terrific puff. Unexpectedly, the tank blew the rubber hose completely across the room. A heavy volume of gas unloaded itself upon the startled gangsters.
For a moment confusion raged; then one man made a grasp for the control handle. To use it, he placed his face directly above the opening in the tank.
The overpowering fumes were too much for him. The flow was powerful, and the gangster staggered. He lost his grip upon the handle and fell to the floor.
No one attempted to do the job that had failed. The remaining gangsters leaped toward the door and yanked it open in a mad endeavor to reach the hall. Their wild rush, mingled with gasping oaths, gave an alarm that could be heard along the entire floor.
Henry Arnaud was waiting. With a swift motion, he pulled open the door of the curio office and stepped into the hall. Then his quick eyes saw a danger spot directly opposite. He could not observe the watching eyes of Felix Zubian and Douglas Carleton, but he knew that such eyes might be there.
Up came Arnaud's automatic. Carleton and Zubian saw it. They knew the hand that wielded it. Within their hiding place, they dived for safety as a bullet crashed through the glass panel just above their heads.
With that shot, Arnaud swung to the end of the hall. The startled gangsters were not unprepared; they had been holding revolvers in readiness, should guns be necessary. Zubian had feared that Arnaud might managed to stagger to safety before the gas had completely overcome him.
Now, in the clear air of the hall, the gangster heard Squint Freston's sharp command. They raised their revolvers, but before they could fire at the figure of Henry Arnaud, a quick burst of shots came from the automatic. Backing along the hall, Arnaud delivered these fatal shots; then he swung down the stairs, ready to meet new
