“That’s right, Mary!” said her father. “I believe you are on the right track.” Just at this moment there was a queer sound, apparently in one corner of the room. “Hark!” said Dr. Corliss. “What was that, Mary?” “It sounded like something rapping on the floor!” said John, with wide eyes. “Oh, I hear sounds like that quite often,” said Mary carelessly. “At first it frightened me, but I have got used to it. I suppose it must be a rat in the cellar.” “Yes, I dare say it is a rat,” said her father. “Old houses like this have strange noises, often. But I have never seen any rats.” “It sounded too big for a rat,” declared John. “Aren’t you afraid, Mary?” “No,” declared Mary; “I’m not afraid, whether it’s a rat or not. Some way, I think I couldn’t be afraid in this room.” “I thought girls were always afraid of rats,” murmured John. CHAPTER VII CALIBAN With rosy cheeks and sparkling eyes Mary returned from a walk with Katy Summers. It had been pleasant but uneventful. Just as she turned in at the little dooryard of home, she thought she spied a black Something dart like a shadow across the little strip of green beside the house. “It looks like a cat,” said Mary to herself. “I will see where it went to.” She followed to the end of the house, where the shape had seemed to disappear. There was nothing to be seen. She went around the ell, and back to the front of the house again. Still there was no trace of the little shadow that had streaked into invisibility. “If it was not my imagination, it must have gone under the house,” said Mary to herself. “Two or three times I have thought I spied a black blur in the act of disappearing; and I believe we are haunted by something on four legs. I will ask the family.” That night at the supper-table she broached the question. “Mother, have you ever seen a cat about the place--a black cat, a swift cat, a cat that never stays for a second in one spot--a mysterious cat that is gone as soon as you see it?” “That sounds spooky enough!” commented Dr. Corliss. “You make the shivers run down my sensitive spine!” “I have not seen any cat,” said Mrs. Corliss. “I think you must be mistaken, Mary.” “Yes, I’ve seen a cat!” volunteered John,--“a thin black cat, oh, so thin! I saw him run across the lawn once; and once I saw him crouching down by the lilac bush near the back door. I think he was catching mice.” “Then there _is_ a cat,” said Mary. “I thought I might be dreaming. He must be very wild. I believe he lives under our house.” “Under the house!” exclaimed Mrs. Corliss. “Surely, we should all have seen him if he lived so near. I can’t think he could have escaped my eyes. But now, I remember, I have heard strange noises in the cellar once or twice.” “I have, often,” said Mary, “under my library.”