The library smelled of old paper and cinnamon from the cakes. It was Halloween night, so the windows glowed with pumpkin smiles. Zosia held a small box with a diode and wires. - 'This is my whisper meter,' she whispered quietly to Tom. The diode was supposed to flash when someone speaks almost silently. - 'Shall we check the cellars? - Tom asked, correcting the wizard's hat on his head. Mr Jurek had warned them in the morning that it was dragging down there. When the diode flashed green, Zosia only nodded. They climbed the narrow staircase, past the door marked Warehouse B. The doorknob was cold, but gave way after a quiet tap. Beyond the threshold, it smelled of dust and apples from the festival. The diode lit up more strongly as they passed a rack of atlases. - Can you hear? - Tom set his ear as if he were fishing for a radio station. Something was tapping in the pipes, once fast, once like a frozen clock. Zosia counted the beats on her fingers and froze. - It's S.O.S. - she said, clutching the box tightly in her hand. At the end of the corridor a small window in the door glowed. A white piece of paper flashed in the glass, like the wing of a bat. On the sheet was a diagram of the shelves and an arrow to the locker. Next to it the inscription: Do not open by yourself. Please do it quickly. Zosia and Tom looked at each other in the dimming light. - I'm counting to three - she whispered quietly. - One, two... Tom grabbed the wheel of the door and the metal hummed deafeningly. Then the diode shone with a steady light, and the lock vibrated. Something moved away on the other side, as if waiting.