Monday's bell at High School No. 7 sounded sluggishly, as if the school needed coffee too. Anka, a high school graduate from Class 4C, swiped her finger across the logbook screen and froze. There was an extra history lesson on the timetable, assigned to room 313A, which she did not associate. There were no lettered numbers throughout the building, and the third floor ended at 312. - Is this a mistake? - whispered Ola, her pew sitter, peering at the screen as if it were a secret cipher. Anka shrugged her shoulders, though her heart sped up as if someone had sped up the metronome in her chest. The doorman, Mr Grzelak, replied briefly that there was no such room and never had been. A moment later came the notification: "Classes moved, room 313A, entrance from the gymnasium side". At the big break, Anka walked around the sports wing, where it smelled of paint and rope dust. The door to the service stairs was closed, but from behind it came the scrabble of chalk across the blackboard. Through a gap in the mesh, she saw a dark hall and a green sheet on which letters glided. The letters, as if guided by an invisible hand, formed the phrase: 'Do not open'. After lessons, she stayed in the library, sorting through a stack of yearbooks of the school magazine with Mrs April. In the bound evacuation plans from the 1930s, she found a drawing of a wing that was no longer there. Room 313A, signed as the History Study, and the stairs by the gymnasium were marked in red. Someone had added in pencil in a small hand: "Closed until further notice, 1937". In the evening, the corridors were deserted and only the buzzing of fluorescent lights and the echoing footsteps of the janitor could be heard from the cloakroom. Anka slipped out of the library, turned by the cups and stood in front of a narrow door with a tarnished handle. On the metal plate, which she saw for the first time, was stamped in cool letters: 313A. The phone vibrated in her hand, showing a new message from an unknown sender: "Do not open. Not yet." From behind the door someone whispered her name, very clearly, as if standing right next to her ear. Anka tightened her fingers on the door handle as the lock from inside clicked twice.