“One moment!” he called.
I paused and turned, directing the ray of my torch upward. He was fumbling in a sort of little cupboard at the head of the steps, and from it he presently extracted his shoes, and proceeded to put them on, talking rapidly the while.
“It was touch and go when that black devil came up, Greville. I also was black from head to feet; black robe, black socks, and a black head cover, made roughly from a piece of this old gibbeh, with holes cut for eyes and mouth! He didn’t see me, and he couldn’t hear me. I dodged him all round the gallery like a boy dodging around the trunk of a tree! When he made fast the line, on the end of which I could see two large iron hooks, and lowered it, I recognized the method.”
He had both his shoes on now and was busily engaged in lacing them.
“It confirmed my worst suspicions—but this can be discussed later. Having lowered it to its approved length, he swung it like a pendulum; and presently it was caught and held by someone hidden behind a window of the mosque. You will find, I think, that there is a still lighter line attached to the hooks. This enabled the Negro, having swung across from the mosque to the house, to haul the pendulum back until the box was safely disposed of. It was as he swung across in turn, that I got busy with the wire cutter.”
He came clattering down, and:
“Left!” he said urgently—”into the mosque.”
I found myself proceeding along that narrow, mysterious passage.
“Light out!”
As I switched the torch off, he opened a door. I was looking along a flat roof, silvered by moonlight—the roof of the mosque.
“I hit him just before he reached this door. There’s a bare chance he may have left a clue.”
“A clue to what?”
A considerable group of people had collected in the street, far below, including, I thought, Armenians from across the river, as many excited voices told me. But I was intent upon the strange business in hand; and:
“The sound!” said Nayland Smith; “that damnable, howling sound which was their signal.”
No torch was necessary now. The roof was whitely illuminated by the moon. And, stooping swiftly:
“My one bit of luck to-night,” he exclaimed. “Look!”
Triumphantly, for I could see his eyes gleaming, he held up an object which at first I was unable to identify, I suppose because it was something utterly unexpected. But presently recognition came. It was a bone...a human frontal bone!
“I’m afraid,” I said stupidly, “that I don’t understand.”
“A bull-roarer!” cried Nayland Smith. “Barton can probably throw light upon its particular history.”
He laughed. A length of stout twine was attached to the bone, and twisting this about his fingers he swung the thing rapidly round and round at ever increasing speed.
The result was uncanny.
I heard again that awesome whining which had heralded the death of Van Berg, which I had thought to be the note of some supernatural nocturnal creature. It rose to a wail— to a sort of muted roar—and died away as the swing diminished....
“One of the most ancient signaling devices in the world, Greville—probably prehistoric in origin. Listen!”
I heard running footsteps, many running footsteps, in the street below—all receding into the distance....
Sir Denis laughed again, shortly.
“Our bull-roarer has successfully dispersed the curious natives!” he said.
CHAPTER THIRTEENTH
THE BLACK SHADOW
Dawn was very near when that odd party assembled in the room which we used as an office, the room in which Van Berg had died. Nayland Smith presided, looking haggardly tired after his exertions of the night. He paced up and down continuously. The chief stood near the door, shifting from foot to foot in his equally restless fashion. Rima sat in the one comfortable chair and I upon the arm of it.
A Persian police officer who spoke perfect English completed the party.
“Dr. Van Berg, as you know,” said Sir Denis, “died in this room. I have tried to explain how the murderer gained access. The room being higher than Sir Lionel’s, the line used was shorter, but the method was the same. I found fingerprints and footmarks on the roof of the mosque and also on the ledge below these shutters. A man stabbed as Van Berg was stabbed bleeds from the mouth; therefore I found no bloodstains. The Negro was swung across, not from the window, but from the roo/’ofthe mosque. He employed the same device, having quietly entered, of spraying the head of the sleeper with some drug which so far we haven’t been able to identify. It smells like mimosa. Fortunately, a portion remains in the spray upon the dead African, and analysis may enlighten us.”
“But Dr. Van Berg was stabbed, as I remember?” said the Persian official.
“Certainly!” Nayland Smith snapped. “He had a pair of Caspian kittens sleeping at the foot of his bed. The bed used to stand there, just where you are sitting. They awakened immediately and in turn awakened him. He must have realised what was afoot, and he sprang straight for the box. It was his first and only thought—for already he was under the influence of the drug. The Negro knifed him from behind.”
He pointed to a narrow-bladed knife which lay upon a small table.
“He came provided for a similar emergency to-night....
That unhappy mystery, I think, is solved.”
“I cannot doubt it,” the Persian admitted. “But the strength of this material,” touching a piece of the slender yellow-gray line, “is amazing. What is it?”
“It’s silkworm gut,” Sir Lionel shouted. “I recognized it at once. It’s the strongest animal substance known. It’s strong enough to land a shark, if he’s played properly.”
“I don’t agree with you. Barton,” Nayland Smith said quietly. “It certainly resembles silkworm gut, but it is infinitely stronger.”
Before the chief could reply:
“A very singular business. Sir Lionel,” the suave official murmured. “But I am happy to leam that no Persian subject is concerned in this murderous affair.”
There was a pause, and then:
“A fourth man was concerned,” said Nayland Smith, speaking unusually slowly. “He, as well as the Negro whom I wounded, has managed to get away. Probably there are exits from the mosque with which I am unacquainted?”
“You suggest that the fourth man concerned was one of our subjects?”
“I suggest nothing. I merely state that there was a fourth man. He was concealed in a window of the mosque.”
“Probably another of these Negroes—who are of a type quite unfamiliar to me....”
“They are Ogboni!” shouted the chief. “They come from a district of the Slave Coast I know well! They’re members of a secret Voodoo society. You should read my book The Sorcerers of Dahomey. I spent a year in their territory. When I saw that bull roarer there—” he pointed to the frontal bone with the twine attached, which also lay upon the small table—”it gave me the clue. I knew that these West African negroes were Ogboni. They’re active as cats and every bit as murderous. But I agree with Smith, that they were working under somebody else’s direction.”
The Persian official, a dignified and handsome man of forty-odd, wearing well tailored European clothes, raised his heavy brows and smiled slightly.
“Are you suggesting. Sir Lionel,” he asked, “that the religious trouble, which I fear you have brought about, is at the bottom of this?”
“I am,” the chief replied, glaring at him truculently.
“It’s beyond doubt,” said Nayland Smith. “The aim of the whole conspiracy was to gain possession of the green box.”