In Torun, in the shadow of the crooked tower, the planetarium smelled of dust and ozone after the rain. Seventeen-year-old Matilda, the granddaughter of a watchmaker, was cleaning up the tired back room after a noisy Science Night. In a cardboard box of old projectors, she found her grandfather's pocket watch, heavy and stubby. One minute mark on the dial was cracked, as if the enamel bore a fine, livid scratch. Janek from the robotic wheel spun around next to it, pretending to count the light bulbs in the ceiling. - Did it dent your time? - He chuckled half-jokingly, seeing her concentration and the disturbing glare of the glass. The physics teacher, Mr Rylski, asked them to leave the Foucault pendulum alone overnight. Matilda, however, noticed the engraving on the envelope: Don't undo it; strain within yourself tomorrow. At twenty-two she pressed the button, just for a test, listening to the watch breathe. The pendulum in the room hovered for a fraction of a second, then vibrated against expectation. Dust danced in a spiral, the star projector blinked and showed a sky with a different density of light. The cracked minute hand glowed milky and the hands wailed in a quiet metal vibrato. - 'That's not a normal resonance,' whispered Mr Rylski, extending his hand but hesitating. Matilda pushed the watch away and noticed the small numbers inside the drawing: 19-06-1963, plus modest coordinates. - 'Don't touch that again,' warned Janek, as the blue security signal flashed in the doorway. - 'I'll talk,' chuckled Mr Rylski, taking the badge, and Matilda felt the tension like a spring. Instead of closing the envelope, she tightened the lace all the way and heard a sound like glass breaking. The lines on the floor parted with a quiet click, matching the scratch on the dial. The technical doors opened of their own accord, and beyond them was not the usual planetarium corridor. They could see posters printed in ink, slogans from yesteryear and a clock that was stubbornly ticking slower. From outside came the sound of engines of another era and a language, seemingly Polish but a little harder. The crackle of the security siren reverberated far away, as if it had lost its way, and everything trembled. Before Matilda could take a step, a cool streak of light and a whisper cut the air: You're back, at last. Janek grabbed her jacket, but the material shifted as if in water. - 'Don't come in, it might smear you,' he said, and his voice sounded double. Mr Rylski returned with his bodyguard, but they both looked straight through the door as if they were not there. The watch pounded a backwards rhythm in his heart, each second awakening the taste of metal on his tongue. A shadow was outlined in the streak of light, the slender profile of a woman and a distinctive mole above her mouth. Matilda remembered a photograph from her grandfather's workshop, signed: 'Sample I - copy, July'. The shadow moved his lips and spoke her name as if he had just made it up. The light broke into two paths and the pendulum hovered between them like a pointer. Matilda tightened her fingers on the lace and moved her foot towards the gap.