Lena is seventeen years old and hosts a school podcast about urban legends. She and Oskar record at night, because that's when the voices always sound most real. In autumn, the city fades faster and the fog covers Spruce Street like a quilt. Today they want to check out the Echo Tunnel, closed for years after a wall collapsed. There was a rumour that the echoes in it don't echo, but respond with other people's words. The entrance looked like a mouth, framed by graffiti and a crooked warning sign. Lena held up the microphone, while Oskar smoothed the former lines on the concrete with a torch. "Sounds like the intro of the season," he muttered, trying to dispel the silence before the first step with a joke. A bat flew from the shadows, leaving behind a waft of sudden cool air. A plaque at the entrance recalled a disaster decades ago and a quick, makeshift renovation. Inside, it smelled of rust and water oozing from cracks in the vault. The echo caught their footsteps and returned them as if with a different sequence of beats. Someone had left chalk arrows on the wall earlier, fresh and still dusty under their fingers. "Let's mark the way," Lena whispered, pulling a red poster chalk from her pocket. Oskar drew an X every dozen steps or so, and the lights flashed as if counting. After a turn, they found a rucksack leaning against a rusty beam, with one zip open. Inside lay a maths notebook, a bus ticket with today's date on it and a metal thermos. Lena unscrewed the cork; the steam hit her fingers, still warm and sweet. "Hello?" called out Oskar, and the echo sent back a word no one had said to them. A short "Lena" came back from the darkness, said in a voice similar but shifted by half a tone. They stopped at the same time, feeling the sound pass through their clothes, like wet fabric. The recorder murmured a noise, and a new track flashed on the screen with tomorrow's date. The arrow they had drawn a moment ago was now pointing in the opposite direction, as if it had changed its mind. "Don't turn around," whispered something just behind Lena's back, calmly, clearly, not asking for an answer. And then, from the depths of the tunnel, her own ringtone melody flowed, broken off after three notes. Lena grabbed the phone, but the screen was dead, as if someone had taken its heart out. A message from an app he'd never installed vibrated in Oskar's pocket. A dot with their names appeared on the map, moving opposite them. "It's probably a reflection of the signal," he tried, but his voice broke, without his usual courage. A shadow, no bigger than a man, ran out of the darkness, carrying something glowing in its hand.