At first Don Alford had some trouble locating the POSAT headquarters. It seemed to him that the block in which the street number would fall was occupied entirely by a huge sprawling warehouse, of concrete construction, and almost entirely windowless. It was recessed from the street in several places to make room for the small, shabby buildings of a wholesale pharmacy, a printer's plant, an upholstering shop, and was also indented by alleys lined with loading platforms. It was at the back of one of the alleys that he finally found a door marked with the now familiar emblem of POSAT. He opened the frosted glass door with a feeling of misgiving, and faced a dark flight of stairs leading to the upper floor. Somewhere above him a buzzer sounded, evidently indicating his arrival. He picked his way up through the murky stairwell. The reception room was hardly a cheerful place, with its battered desk facing the view of the empty alley, and a film of dust obscuring the pattern of the gray-looking wallpaper and worn rug. But the light of the summer afternoon filtering through the window scattered the gloom somewhat, enough to help Don doubt that he would find the menace here that he had come to expect. The girl addressing envelopes at the desk looked very ordinary. _Not the Mata-Hari type_, thought Don, with an inward chuckle at his own suspicions. He handed her the letter. She smiled. "We've been expecting you, Dr. Alford. If you'll just step into the next room--" She opened a door opposite the stairwell, and Don stepped through it. The sight of the luxurious room before him struck his eyes with the shock of a dentist's drill, so great was the contrast between it and the shabby reception room. For a moment Don had difficulty breathing. The rug--Don had seen one like it before, but it had been in a museum. The paintings on the walls, ornately framed in gilt carving, were surely old masters--of the Renaissance period, he guessed. Although he recognized none of the pictures, he felt that he could almost name the artists. That glowing one near the corner would probably be a Titian. Or was it Tintorretto? He regretted for a moment the lost opportunities of his college days, when he had passed up Art History in favor of Operational Circuit Analysis. The girl opened a filing cabinet, the front of which was set flush with the wall, and, selecting a folder from it, disappeared through another door. Don sprang to examine the picture near the corner. It was hung at eye level--that is, at the eye level of the average person. Don had to bend over a bit to see it properly. He searched for a signature. Apparently there was none. But did artists sign their pictures back in those days? He wished he knew more about such things.