Lena closed the study door on the night bolt and switched on the treatment lamp. The autumn rain drummed against the signboard with a smile, and eucalyptus was in the air. Tomorrow, she was to give a workshop to her peers about oral hygiene at her high school. She put up posters on the counter: two-minute brushing, flossing, limiting sugary snacks after school. Her mum, a dentist, had left her a microscope and plaque stainer to record short shots. The clinic was empty, with only the steriliser purring in the steady, soothing tone of the evening. She positioned her phone carefully over the sink on the tripod and clicked record. She rinsed her mouth with fluoride liquid and then brushed as per the instructions: short strokes at the gum line, soft toothbrush, twice a day. She slipped the floss between the four and five, unhurriedly, with a slight twist of the wrist. With the scraper, she dragged it over her tongue until she breathed in a fresh, cool air, without a metallic aftertaste. Finally, she chewed the staining tablet and stood by the mirror, the purple flecks flashing like stars. Out of curiosity, she picked up a bit of plate from the stained area with a toothpick, spread it on the slide and slid it under the microscope. She expected chaotic speckles of bacteria, and saw pulsating dots, as if someone was transmitting a code. The plastic scaler head in the cabinet trembled, although no one touched it. Lena held her breath and pulled the lens back, the points arranged in four groups of short and long flashes. She knew this from scouting because she had once learned the Morse alphabet: L, E, N, A. She thought of the joke and checked the wires, but everything was thoroughly disconnected. For peace of mind, she caught up with the thread still shot, aiming for the narrow space near the bottom seven. The thread snagged on the hard tarnish, twitched like a string and let go, leaving a pattern of purple dots on the white tray. From above, it looked like a blueprint of the school: corridor, auditorium, arrow, 9 p.m. The phone vibrated, number unknown, message a short sentence: Don't be late. Take a toothbrush. - Hello, who's there? - she darted towards the door, more for courage than an answer. A shadow flashed behind the milky glass and the handle twitched slightly, as if trying to remember the movement. Then the microscope flashed with a cold light and the dots on the slide began to rearrange themselves. The letters spread out to form a single word, which Lena read in a whisper: NOW. She squeezed the soft brush in her hand like a torch and took a step into the darker corridor as the key from outside turned in the lock.