Lena always entered school earlier than the rest, out of habit and curiosity. On this September morning, the corridor smelled of paint after the renovation, and the bell sounded different. Not the usual, metallic and flat, but deep, as if it resonated longer in the walls. The phone beeped, reminding her of a physics class and an after-school newspaper editorial board meeting. Then she noticed a new sign above the stairs: "Hall 0 - service entrance, do not enter". Yesterday this placard was not there, she would have sworn on her favourite physics mug, Mrs Zarębska. At the big break, Bartek from the third bench pointed to the clock by the gatehouse. The hands trembled, stopped at 10:17, then moved back a minute. - 'Do you see that, Leno? - He whispered uncertainly, as if he was afraid of setting off an alarm. Lena nodded, as her phone also choked in time and showed 'no network'. The new ringtone was ringing in her ears, though no one else was commenting on it. In the library she found a yearbook from fifteen years ago, yellowed, with an evacuation map of the building. Between the pages lay a sheet of paper with the notation: "Lesson Zero - for those who can hear only". The arrow pointed to a narrow door behind the vice-principal's office, apparently bricked up after a fire. Mrs Grochowska, standing in the threshold, shifted her gaze to Lena, and Bartek tucked his notebook away. - 'To the hall, dear ones, the corridors like to eat up latecomers,' she said, smiling as if for the lens. After three lessons, the building seemed to swell, the corridors lengthened by invisible turns and repetitions. Lena counted windows so as not to lose direction, and Bartek noted tiles like coordinates. The bell sounded again, longer than it should have, until the words in the notebook began to ripple. Dust fell from the ceiling, and a ribbon of mist appeared above the staircase connecting the old wing. From this mist emerged a sign that had not been there before: "To Hall 0 - this way". - 'If it's a high school graduation prank, it's brilliant,' muttered Bartek, but he kept close to Lena. They passed through a technical door that gave way without a key, and entered a narrow service corridor. The lamps blinked with the rhythm of that bell, the phone showed 10:17, as if the digits could not be scrolled. A foil curtain hung at the end of the corridor, and quiet voices could be heard behind it. One of them said her name, very clearly, like an attendance list. Lena raised her hand to push back the foil when her phone vibrated with an unfamiliar message. The screen brightened: "Welcome to Lesson Zero, Lena. Please come in yourself."