I am fourteen years old and have braces on my teeth that sparkle like neon. My name is Lena and I live above the clinic, in a block that smells of paste. On the ground floor is the school's dental surgery, the heart of our Smile Without Secrets campaign. For the past week, something has been going on there that doesn't make me feel at ease. After evening brushing, the sonic toothbrush vibrates in a different way, as if it is transmitting a signal by tapping. The app measuring two minutes suddenly stretches the time, showing unexplained skipped zones. A loop of floss moves on a hook, even though the window is closed. Even the rinse liquid bubbles, forming shapes in the foam like letters. And every time I turn off the light, I smell a fresh mint, although no one has rinsed. There's a rumour at school about the Sugar Whisperer, who spoils breaths before performances. I have a debate tomorrow, so I watch every thread, every movement and every second. My friend Olek says it's a viral campaign, not the ghost of plaque. The hygienist, Ms Kaja, asks us not to panic and to remember to floss. But this morning I found a fingerprint on the mirror, as if someone had written: SMILE. In the evening I take my toothbrush, floss and a small dental mirror, and go downstairs. The corridor of the clinic is empty, only the clock is ticking as the countdown to two minutes. The surgery door is closed; the blue light of the steriliser blinks from behind the milky glass. When I touch the handle, my toothbrush turns on by itself and points its head towards the lock. The vibrations form a Morse rhythm, very distinct: two short, one long, a pause. I hear something scrubbing at the rinse cup, retracting and freezing. The lock clicks, the door gives way and the air hits me with a chill and an intense mint. On the wall, above the tap, flickers an inscription arranged in foam: DON'T COVER UP YOUR SMILE. Someone, or something, answers me with an even louder buzz, as if waiting for a question. I take a breath so fresh it tingles, and put my foot in the threshold. And a creak comes from the depths of the study, as if someone is moving a huge mirror.