“But how?” came Cardona’s question.
“One came from this floor tonight,” said Biscayne thoughtfully. “There was no one here to mail it.
“Look at the side wall of this room. The mail chute must be on the other side—”
Cardona was tapping at the wall. Eagerly he searched, and the others joined with him. Keen though these men were, the secret mocked them.
“We’ll smash that mail chute!” exclaimed Cardona grimly. “Wait until I get Mayhew. We’ll find it from the other side—”
“Here!” The cry came from Biscayne. He was rapping at the baseboard of the wall. “This may be it!”
Cardona was with the professor. Together, they pried effectively. The small portion of flooring yielded. The baseboard came open.
The little cache was disclosed. The clockwork was still ticking, but now there was no letter projecting from the clips.
Fumbling with the mechanical box, Cardona pried off the lid.
The interior of the box showed a set of thin sections, more than twelve in number, each slightly larger than an envelope.
“One every forty-eight hours,” said the detective to Biscayne. “That’s how it was set—”
“No,” said Biscayne, “it must have been gauged for twenty-four. That’s why the Sutton letter came in between the death notes.
“By leaving empty spaces, the deliveries could be interrupted on days they were not needed.”
“Right,” declared Cardona.
Biscayne began to pace up and down the room. His mind was at work.
“If I had known Harshaw well,” said the professor, “I might have divined some of this beforehand.
“Three men have died because of his fiendish plotting. We can be thankful only that the fourth was saved — my cousin, Arthur Wilhelm.
“Silas Harshaw was unquestionably eccentric,” Biscayne continued. “He imagined enmities, and saw schemes where there were none.
“He wanted to protect that hiding place behind the radiator — that is evident. So he not only made it difficult to find. He placed the apparatus there, to thwart any man who might come.”
“What about Max Parker?” queried Cardona.
“A cross-purpose,” responded Biscayne. “There might be a connection between Max Parker and Homer Briggs. It seems evident that Parker must have blundered in upon the trap that was laid for others.”
“IF he was an enemy, the old man would have mentioned it,” commented Cardona. “How do you figure that Harshaw worked the big killings? He must have bumped himself off to start.”
“Undoubtedly,” declared Biscayne. “Knowing that he had not long to live, he used his own trap for suicide. But he must have wanted the others to die, too.
“Take Glenn, for instance. The old man was a chemist. Those cigarettes which—”
“I was right,” interrupted Cardona. “Harshaw must have got a couple of packs — we found one in the strong box, here. Then he must have planted it in Glenn’s Tuxedo; that box that Glenn had with him.
“One poisoned cigarette in the box! That’s what did it. I had it right. But how did Harshaw put it there the box — in the Tuxedo—”
“That we may never learn,” replied Biscayne. “We have the motive. We have evidence. That is sufficient for the present.
“Let us consider Thomas Sutton. The old man went to his house, according to the letter. He must have heard Sutton speak about the cane.
“He must have noticed that closet door. He was a shrewd man, was Silas Harshaw.”
“We’ve linked him there,” agreed Cardona. “We’ve already tied him up with Throckmorton. Do you think he fixed the hose on the gas lamp?”
“In all probability,” said Biscayne. “Of course, a man was discovered in Throckmorton’s home. There are details that are still bewildering.
“The attempt upon my cousin Arthur’s life tonight, however, settles the case against Silas Harshaw.
“That bomb is crudely fashioned. Perhaps it was made in the old man’s workshop, right here.”
“We’ll look!” cried Cardona.
“Not yet,” said Biscayne. “We have work to do first. Perhaps there is more to find.”
“The old man’s model?”
“Yes.”
Cardona looked around the room. He spied the closed radiator. He turned quickly to Biscayne.
“That shooter behind the radiator!” he exclaimed. “It wasn’t there just to keep people from finding a few papers and envelopes. That’s where the model is, I’ll bet!”
Eagerly, the detective pulled the knob of the radiator and opened the sections.
He realized again the efficiency of this trap. A man shot here would topple backward — falling, he would lose hold, and the radiator would close!
It had happened with Silas Harshaw. It had happened with Max Parker. But it could not happen now, since the clamped revolver had been removed.
Peering in the light of his torch, Cardona spied the flat bottom of the shallow hole inside the wall.
His fingers pried, and were rewarded. The bottom of the strong box swung upward. The glow of the flashlight spotted a square wooden box.
Dropping his light, Cardona drew the box out and set it in the middle of the floor. He lifted the lid.
Inside was a metal device, more than one foot square. It seemed strangely light as Cardona removed it from the box.
It had dials and knobs, with little posts for the attachment of wires.
It was the model of the remote-control machine — the invention of which had been the life work of Silas Harshaw!
CHAPTER XXII
THE SHADOW INTERVENES
PROFESSOR ROGER BISCAYNE took immediate charge. The discovery of the remote-control machine was of the greatest moment now.
The details of the killings could be worked out later. For Silas Harshaw, dead, could no longer be a menace:
His work was ended; his fiendish schemes had been disclosed, made harmless forever.
The little model, with its complex contrivances, was a perplexing subject.
Biscayne had the paper that showed the plan, but as he compared the diagrams with the metal box, he saw discrepancies.
His knowledge of Silas Harshaw’s mechanical methods might avail, however. Roger Biscayne was the only man who could solve the intricacies of the device.
After several minutes of studying the device and the plans, Biscayne pressed various knobs with no result. The machine was not hooked up; but he seemed to be hoping for some action. None occurred.
Biscayne ended his experiments for the moment. He asked to see the papers that had been found within the hole behind the radiator.
Cardona produced them.
One sheet bore a short, written reference that said, “Model.” Beneath it were these words:
Keys to arrangements are in drawer E.
“Drawer E,” said Biscayne thoughtfully. “Where is that? Ah! I recall! There are some drawers in the workshop. They are designated by letters. Will you find it, Cardona?”
“Sure,” said the detective.
He was starting for the door when Biscayne called him.
“Wait,” said the professor. “I’ll go with you. There may be something else, of importance in there. You can keep looking after I come back to continue with my experiments.”
As he reached the door, Biscayne turned thoughtfully and pointed to the model on the floor.
“That plug is evidently arranged for an electrical connection,” he remarked. “If you screw it into the outlet by the table, it will save time.”
Commissioner Weston picked up the model and carried it carefully toward the wall.
Biscayne left the room, accompanied by Cardona. The door closed behind them.
Weston removed the plug of the table-lamp wire from the plug hole in the baseboard.