The Amulet of Samarkand

Underwood was evidently still talking, his mouth close up to the receiver. Nathaniel applied an improving Shock to the disc, at which the imp's face appeared.
    "Hoi, there was no call for that!"
    "The sound, where's the sound?"
    "He's whispering, ain't he? I can't hear a thing. And it ain't safe to go any closer."
    "Let me hear it!"
    "But, boss, you know there's a safe limit. Magicians often have protective sensors; you know, even this guy—"
    Nathaniel's face felt sore and puffy under the strain. He was past caution. "Do it. You won't want me to ask again."
    The imp did not answer. Underwood's face reappeared, so close it almost filled the center of the disc. The hairs tufting from his nostrils were rendered in loving three-dimensional detail. The magician was nodding. "I agree. I suppose I should be flattered... Yes, looking at it that way, the boy is a testimony to my hard graft and inspiration. Now, my old master—"
    He broke off, with a wince and a shudder, as if something cold had brushed against him. "Sorry, Grigori. It was just, I felt—" Nathaniel saw the eyes narrow, the familiar brows beetle sharply. At this the image on the disc suddenly broadened out, as if the imp were retreating hurriedly across the room. Underwood uttered a loud syllable; the imp's voice tried to copy it, but cut out midway, as if turned off like a radio. The image remained, quivering strangely.
    Nathaniel couldn't suppress a catch in his voice. "Imp, what's happening?"
    Nothing. Silence from the imp.
    "I order you to leave the study and return to me."
    No answer.
    The image in the disc was not reassuring. Shaky though it was, Nathaniel could see Underwood putting down the telephone, then slowly rising and coming round to the front of his desk, all the while peering hard—up, down, in every direction— as if hunting for something he knew was there. The image shook still harder: the imp seemed to be redoubling its efforts to escape, but to no avail. In mounting panic, Nathaniel applied a few frantic Shocks to the disc in vain. The imp was frozen, unable to speak or move.
    Underwood crossed to a cupboard at the back of the study, rummaged within it, and returned, carrying a metal cylinder. He shook it: from four small holes at its top, a white powder was emitted, which quickly spread out to fill the room. Whatever the powder did, the effect was immediate. Underwood gave a start and stared upward—directly at Nathaniel. It was as if the disc was a window and he was looking directly through it. For a moment, Nathaniel thought his master could actually see him, then he realized it was simply the suspended imp that hung revealed.
    Horror-stricken, Nathaniel watched his master bend down to the carpet and pull at a loop of ribbon. A great square section of carpet peeled up and fell away to one side. Below were two painted pentacles. His master stepped inside the smaller, never for one moment taking his eyes away from the frozen imp. He began to speak, and within seconds a tall misty apparition appeared within the larger circle. Underwood uttered a command. The apparition bowed and vanished. To Nathaniel's amazement, Underwood's body seemed to shimmer and slide away from itself. His master still stood within the pentacle, but another version of his master, ghostlike and see-through, stood alongside it.
     
    The ghostly form lifted into the air, kicked its heels and began to float forward—straight to where the helpless imp was still relaying the view from the study. Nathaniel screamed commands and shook the disc in fury, but could do nothing to stop his master's slow approach. Closer, closer... The spectral eyebrows were lowered, the glinting eyes never looked away. Now Underwood's form swelled to fill the disc—it seemed as if it would break right through....
    Then nothing. The disc showed the study again, with Underwood's physical body still standing motionless in the pentacle.
    Despite his panic, Nathaniel knew all too well what was happening. Having located the spy and safely frozen it in position, Underwood had decided to follow the imp's astral cord back to its source to learn the identity of the enemy magician. Such sources might be many miles away; perhaps his master was expecting a long journey in his djinni-controlled form. If so, he was about to get a surprise.
    Too late, Nathaniel realized what he had to do. The window! If he could throw the disc out into the street, perhaps his master would not guess....
    He had only taken