The rain tapped against the stained-glass windows of the old library, casting prismatic shadows over the dust motes swirling in the air. Clara pushed her wire-rimmed glasses higher up her nose and adjusted the yellowed cardigan she’d worn since moving into the attic apartment three months ago. Her fingers brushed the edge of the leather-bound ledger on the oak desk when something metallic caught her eye – a half-forgotten key tucked between the pages. The same key she’d seen in the pocket of her father’s coat when he died, the one that had vanished during the整理 of his study.

The key turned in her palm with satisfying precision, unlocking a hidden compartment in the desk. Inside lay a faded photograph of a young woman in a military uniform, her face partially obscured by a cap. Clara’s breath caught when she recognized the font of the letterpress stamp – the same used by the intelligence agency her grandmother had worked for during the war. The photograph was dated 1943, two years before her grandmother’s disappearance.

Her phone buzzed on the desk, lighting up the room with a cold blue glow. A message from her landlady: The gas leak in the basement is contained, but the pipes are corroded beyond repair. You’ll need to vacate by next week. Clara’s stomach dropped. The attic apartment had been her sanctuary, a place where she could escape the memories of her mother’s suicide and the whispers about her father’s secret past. But now she had to leave, and the key in her hand suggested there was more to uncover.

That night, Clara found herself standing in the dimly lit basement, the key in her fist. The air smelled of mildew and ancient wood. In the corner, behind a stack of rusted filing cabinets, she spotted a steel box embedded in the wall. The combination lock had been tampered with – someone had filed down the numbers to 3-14-7. Her grandmother’s birthday. The key fit perfectly, turning with a faint click.

Inside the box were three items: a letterset, a cipher wheel, and a letter written in her grandmother’s looping script. Clara spent the next two days decoding the message, her fingers worn from turning the cipher wheel. The letterset revealed a list of names – all connected to her father’s childhood friends. The final entry was her own name, circled in red ink. The letter explained that her grandmother had been guarding a secret project during the war, one that had been stolen by a traitor. Her father had been tasked with recovering it, but he’d been killed before he could complete the mission.

On the third morning, Clara stood in the middle of the attic with a suitcase and a sense of dread. Her landlady was waiting in the doorway, holding a police file. The contents of the basement had been discovered during the gas leak investigation. The steel box was gone, along with the key. The file contained pictures of Clara’s father in a military uniform, his face crossed out with a red mark. The final page was a newspaper clipping from 1945, reporting the execution of a man named Viktor Ivanov for espionage.

Clara’s phone rang in her pocket. It was her best friend, Sophie. You need to see this, she said. The police found a hidden room in the attic. They say it’s connected to your father’s case. The line went dead before Clara could ask questions. She packed the key into her suitcase, ignoring the cold spot where the steel box had been, and stepped into the rain. The library’s stained-glass windows glowed in the distance, their colors bleeding into the gray sky like a warning.