“What do you mean?” inquired Barth.
“He means,” came Cranston’s steady response, “that you are accepting the note on the value of its typewritten signature. Mr. Darring, apparently, still holds to his opinion that Crofton’s disappearance was a hoax.”
“I do,” declared Darring abruptly. “We came here for a second experiment. Professor Lessep has avoided it. In my opinion, this devisualization stuff is still hypothetical. Anybody could have typed that note. Whoever did type it could have been seen, as well as heard.”
“I was here from one until five,” declared Lessep solemnly. “I saw no one in the laboratory during those hours.”
“And you returned at seven thirty.”
“Yes. With Mr. Warlock.”
“And after that?” queried Barth, swinging to Warlock’s way of reasoning.
“The two of us were here,” affirmed Lessep, “until eight o’clock. Then I went out to admit you, commissioner. I left Mr. Warlock here alone.”
“For about five minutes,” interjected Warlock. “I was in the laboratory all that while. I heard no sounds of typing.”
“This business is serious,” announced Barth, glaring about the group. “Here is new evidence that can not be minimized. If this should be a hoax” — he paused to nod approvingly toward Darring — “I intend to treat it as an actual crime.
“Let us forget Miles Crofton for the moment. You were here, professor, four hours this afternoon. You could have typed that note. You could also have removed the parts from the machine.”
Lessep began a protest. Barth silenced him with a fierce gesture. The commissioner then turned to Warlock.
“You were here also!” thundered Barth. “Alone, for five minutes. A short time yet sufficient to have done the work. Jove! This talk of an unseen man is maddening me. I intend to deal with those who are visible. Who else was in here alone?”
“I was,” replied Darring, calmly. “While we were searching for the lost lever—”
“That was after the message was found,” interrupted Barth. “After the lever was stolen. I mean before we discovered this note.
“Who else was here beside you two?” He glared at Lessep; then at Warlock. “Who else could have been in here?”
“Miles Crofton,” replied Darring.
“MILES CROFTON?” spluttered Barth, in total surprise. “But — but you, Darring, you were the one who termed it all a hoax. You claim that Crofton could not have become unseen—”
“I still hold my claim,” responded Darring. “But do not forget, commissioner, that there was an interval between five o’clock and seven thirty, while neither the professor nor Warlock happened to be here.
“Neither you nor I could have been here during that period, for you met me at my office at five and we dined together. But Crofton could have come here. Not unseen, but visibly. Or he could have sent some one. Any one who had a duplicate key.”
“That’s right,” admitted Barth. He mopped his forehead with a silk handkerchief. “This whole case is maddening. It brings us in circles, back to where we started. I don’t know where it will end, unless—”
“Unless,” completed Darring, in his skeptical tone, “the professor gives us proof that his devisualization is fact, not fancy. Just how long, professor” — he wheeled to Lessep — “would it require for you to replace that missing lever?”
“Some time,” responded Lessep, in a troubled tone. “It is a vital portion of the mechanism.”
“How vital? Just what is the mechanical principle involved?”
“That is my secret,” pleaded Lessep.
Darring looked hopelessly at Barth. The commissioner towered in indignation. He waved his hand toward the laboratory.
“Come, Lessep!” he ordered the professor. “This is no time for secrets. I shall guarantee protection to your invention. But unless you are willing to cooperate, I shall order your arrest.”
THEY entered the laboratory, and formed a group about the first motor. Lessep reluctantly began to point out mechanical features of the device. His words became incoherent. Barth became brusque.
Lessep pleaded.
“I am afraid,” he declared. “Crofton is a menace.”
“Proceed with your explanation,” insisted Barth.
“It is useless,” crackled Lessep. “So much depends upon the missing part. You would have to see it.”
“We have seen the photographs,” remarked Darring.
“Yes, professor,” urged Warlock, suddenly. “Bring the photographs. Let us see them. They will do to illustrate the use of the connecting lever.”
Lessep rubbed his chin. At last he nodded. Turning from the group he entered the little office. Ceiling light and desk lamp had been extinguished. The professor turned on the ceiling light; then closed the door behind him.
Lamont Cranston was examining the tall glass cabinet. He had noted that its sides were attached by clamps midway on each edge. As he unfastened clamps at the sides, the rear wall pivoted on its upper and lower fastenings; then swung back into place at Cranston’s touch.
“I really believe,” Barth was saying solemnly, “that the professor’s fears are justified. Accept my apologies, Warlock, for accusing you the way I did. Actually I was not accusing; I was merely speculating. I wanted to find some solution other than the obvious.”
“The obvious?” inquired Darring.
“Yes, the obvious,” stated Barth. “For here the incredible happens to be the obvious. It sounds impossible to think that a man could be surrounded by an atmospheric condition that renders him invisible. Yet analysis tells me that Miles Crofton is actually devisualized.
“Professor Lessep knows it. That is why he fears. He realizes that Crofton — an unseen killer — could strike him down with some invisible weapon.”
“You are right, commissioner,” spoke Warlock. “I knew that you would return to your first impression. It is the only sound explanation.”
“Tommyrot!” ejaculated Darring. “Where is the proof? Lessep could furnish it by repeating his experiment. He has failed to do so. He removed that lever. He wrote that note.
“If Crofton is in the picture — as an unseen killer — why doesn’t he strike? Why should a man in his position fail to follow up a threat? If Crofton—”
Darring never ended the sentence. From beyond the door of Lessep’s study came the sudden muffled boom of an explosion. The laboratory caught the jar. The glass cabinet rattled. Those in the large room almost lost their footing.
WAINWRIGHT BARTH leaped to the door of the office and wrenched it open. With others close behind him, the commissioner was confronted by an outpouring of smoke that came from the corner by the filing cabinet.
Barth staggered back. Then, as the fumes were clearing, he led the way into the office. Lessening smoke enabled the commissioner to see Lessep’s body, prone upon the floor. The filing cabinet was wrecked; the hanging lamp above it was shattered.
Lamont Cranston reached the professor’s body ahead of the commissioner. His keen eyes saw that Melrose Lessep was dead. Barth, also realizing the professor’s fate, turned to stare about the room.
Darring had entered behind Cranston. Now Cardona and Warlock were coming in from the laboratory.
“The Unseen Killer!” cried Barth. “He has caused this. He was here — in this room—”
He looked toward the door, diagonally opposite the demolished filing cabinet. It offered the logical spot from which a person could have projected a bomb or a grenade without danger to himself. Wildly, Barth sprang to that spot, to find nothingness. He headed into the laboratory. Warlock, Darring and Cardona were close behind him.
Staring, the commissioner saw the door that led to the rear hall. It was unbolted and open. Barth pointed, excitedly. Cardona spoke.