On Thursday afternoon Mrs. Clarke, dressed for going out, took her handbag with some money and her key in it, pulled the door behind her to lock it and went to the over 60s Club.She always went there on Thursday. It was a nice outing for an old woman who lived alone.         At six o’clock she came home, let herself in and at once smelt cigarette smoke.  Cigarette smoke in her house?How?How?Had someone got in?She checked the back door and the windows. All were locked or fastened, as usual. There was no sign of forced entry.         Over a cup of tea she was wondering whether someone had a key that fitted her front door—“a master key”perhaps. So she stayed at home the following Thursday. Nothing happened.Was anyone watching her movements?On the Thursday after that she went out at her usual time, dressed as usual, but she didn’t go to the club.Instead she took a short cut home again, letting herself in through her garden and the back door. She settled down to wait.         It was just after four o’clock when the front door bell rang. Mrs. Clarke was making a cup of tea at the time. The bell rang again, and then she heard her letter-box being pushed open. With the kettle of boiling water in her hand, she moved quietly toward the front door. A long piece of wire appeared through the letter-box, and then a hand.The wire turned and caught around the knob on the door-lock. Mrs. Clarke raised the kettle and poured the water over the hand.There was a shout outside, and the skin seemed to drop off the fingers like a glove. The wire fell to the floor, the hand was pulled back, and Mrs. Clarke heard the sound of running feet.