"Is there something I can do for you?" she asked. "Well, we're not exactly sure," one of the men said. "However, we have reason to believe you can." He cleared his throat. "To get directly to the point, we are interested in an explosion which we believe took place on these premises last night." "Oh, dear!" Julie said. "Have the neighbors complained?" "No, Mrs. Pillsworth, nothing like that. You see, we have mechanical means of knowing about explosions. There is a device in existence which records the precise time, location, magnitude and nature of even the slightest explosion anywhere on the Earth's surface. One was recorded here last night. The nature, however, was undetermined and that's why we decided to investigate." Julie nodded. She told them of Marc's basement laboratory and his experiments to make heavy substances lighter than air. She explained about the explosion. "The experiment was a complete failure, I guess," she concluded. "I see," the man said. "Would you mind, though, if we took a look around in the basement anyway?" "No, I don't mind," Julie said. "But judging from what I saw down there last night you won't find anything but a lot of rubble." "Of course," the man said. "But we can't take a chance on a possible new type of explosive. It might be of military interest. Just in case, Mrs. Pillsworth, do you know where your husband kept his notes on the experiment?" Julie thought for a moment. "In a little black book, I believe," she said. "He just left it lying around loose down there." The man nodded and got up. "We'll have the maid show us where it is," he said. "Thank you very much." * * * * * When they were gone, Julie leaned back in her chair and closed her eyes. She was so weary, just from talking to people. Then she sat up quickly. She could have sworn she'd heard something out in the hall, a furtive noise, as though someone had cautiously let himself in the front door. She got up and went to the doorway of the study. "Marc!" she called, then suddenly froze where she was. Never had she seen two uglier customers than the ones that were now cowering before her in the shadows of the hallway. Two very dark little men with gross black beards, thick-lensed glasses and derby hats. They seemed to be exact and very dreadful duplicates of each other, as though the same awful mistake had happened twice. Their eyes shifted nervously before Julie's horrified gaze. They looked precisely like a pair of spies. "Who are you two?" Julie asked uneasily. "What are you doing here?" The two shifted uncomfortably, glanced at each other. Finally the one closest to Julie spoke.