“It’s a ‘he,’” replied Broad calmly, “and I hope I’ll be excused answering your question. I had been in the house an hour when you arrived—I was in the back room, which is empty, by the way. You scared me. I heard you come in and thought it was old St. Nicholas of the Whiskers. Especially when I saw the light go on. I’d had it on when you opened the scullery door—I left that unfastened, by the way. Didn’t want to stop my bolt hole. Well, what do you think?” “About Maitland?” “Eccentric, eh? You don’t know how eccentric!” As the car stopped before the door of Caverley House, Elk broke a long silence. “What are you, Mr. Broad?” “I’ll give you ten guesses,” said the other cheerfully as they got out. “Secret Service man,” suggested Elk promptly. “Wrong—you mean U.S.? No, you’re wrong. I’m a private detective who makes a hobby of studying the criminal classes—will you come up and have a drink?” “I will come up, but I won’t drink,” said Elk virtuously, “not if you offer gin and orange. That visit to the United States has spoilt my digestion.” Broad was fitting a key in the lock of his flat, when a strange cold sensation ran down the spine of the detective, and he laid his hand on the American’s arm. “Don’t open that door,” he said huskily. Broad looked round in surprise. The yard man’s face was tense and drawn. “Why not?” “I don’t know . . . just a feeling, that’s all. I’m Scot by birth . . . we’ve got a word ‘fey,’ which means something supernatural. And it says inside me, ‘don’t open that door.’” Broad put down his hand. “Are you being fey or funny?” he asked. “If I look funny,” said Elk, “I’m entitled to sue my face for libel. There’s something at the other side of that door that isn’t good. I’ll take an oath on it! Give me that!” He took the key from the unwilling hand of Joshua Broad, thrust it in the lock and turned it. Then, with a quick push, he threw open the door, pushing Broad to the cover of the wall. Nothing happened for a second, and then: “Run!” cried Elk, and leapt for the stairs. The American saw the first large billow of greenish-yellowy mist that rolled from the open door, and followed. The hall-porter was closing his office for the night when Elk appeared, hatless and breathless. “Can you ’phone the flats?—good! Get on at once to every one on and below the third floor, and tell them on no account to open their doors. Tell ’em to close all cracks with paper, to stop up their letter-boxes, and open all windows. Don’t argue—do it! The building is full of poison gas!” He himself ’phoned the fire station, and in a few seconds the jangle of bells sounded in the street outside, and men in gas-masks were clattering up the stairs. Fortunately, every tenant except Broad and his neighbour was out of town for the week-end. “And Miss Bassano doesn’t come in till early morning,” said the porter.