It was a December evening and warm gingerbread was smelling. Zosia was hanging lights on the Christmas tree with her dad. Outside the window, snow was swirling and colourful stars twinkled. A red sock full of surprises lay on the carpet. Inside, Zosia found a tiny silver key. Suddenly, a very quiet bell sounded from the fireplace. One light went out and something flashed under the table. Fluffy, the white cat, put up his ears and purred. "Do you hear, kitty?" whispered Zosia, squeezing the key tightly. Tiny, snowy dots appeared on the floor. They led behind the curtain, under the low windowsill in the living room. There, by the letters to Santa, one was missing. In its place lay a card with a small star on it. The card had a castle and a door drawn on it. Zosia lifted the curtain and held her breath for a moment. A tiny round door with a hole in it shone in the wall. The key fitted into them like a lost jigsaw puzzle. Something knocked inside, softly, like a small hammer. "Hello? Who is it?" Zosia asked, putting her ear to it. A whisper and a blast of cold, sweet air answered. The lock clicked, the light spilled out like milk. Zosia turned the key and the door began to swing open.