The rain had been coming down in sheets for an hour straight, soaking through the hem of Sarah’s thrift store cardigan, when she saw the woman on the balcony. She’d cut through the alley behind the 14th Street apartment block to avoid the main road’s puddles, tired from a double shift at the diner, half-asleep on her feet. For a second, she thought she was hallucinating. The woman was leaning over the railing, face tilted up to the rain, and she looked exactly like Sarah. Same cheekbones, same jagged scar on the right thumb from a childhood bike accident, same stubborn curl that always fell over the left eye. Even the oversized flannel she was wearing was the same one Sarah had lost at the laundromat three weeks ago. Sarah opened her mouth to call out, but the woman didn’t hesitate. She stepped off the ledge like she was just stepping down a curb. The sound of her hitting the concrete was dull, lost in the rumble of thunder. Sarah ran, her sneakers slipping on wet grass, screaming for someone to call 911, but the street was empty. By the time the paramedics arrived ten minutes later, the woman was already gone. Sarah hung back by the dumpster, wiping rain out of her eyes, watching them zip the body bag. Her own life was a wreck anyway: eviction notice taped to her door that morning, last hundred bucks stolen from her wallet by her ex-boyfriend, no family in the state who’d care if she disappeared. When one of the paramedics dropped the dead woman’s canvas tote bag near the trash, Sarah didn’t think. She waited until they rolled the gurney away, then snatched the bag up, heart hammering so hard it hurt. Inside was a wallet with a driver’s license: Elena Voss, 26, address in Oak Hill, a neighborhood Sarah had only ever driven through. The photo was Sarah’s face, down to the tiny mole on her chin. No one would look for Elena Voss. No one would miss Sarah Miller. She took the subway to Oak Hill that night, using the crumpled bus pass she found in the tote. Elena’s apartment was a tiny studio on the third floor, neat, smelling of lavender laundry detergent, the same kind Sarah used. She stayed up all night going through Elena’s things, her hands shaking as she pried up the loose floorboard under the bed. There were stacks of manila folders, all labeled in Elena’s messy scrawl. The top one made her breath catch: Hoán Vị (phần 4). She flipped it open. The first page was a spreadsheet. Twelve rows, all with the same photo thumbnail: Sarah’s face. Elena’s name was row 11, marked with a red X. Row 12 was blank, no name yet, just a note: “Candidate located. Phase 4 initiation pending.” Sarah’s stomach dropped. She was row 12. Tucked behind the spreadsheet was a handwritten note: “They’re swapping us out. If you’re reading this, get out before they come for you. Don’t answer the door after 8 PM. Don’t trust the guy at the bodega on 9th. Destroy this file, burn the apartment down if you have to. They call it Hoán Vị – permutation, swapping one for another, like we’re just numbers in a math problem. This folder is the fourth phase of their experiment. They’ve been replacing women who look like us for years, erasing our lives, planting these fake identities so no one notices the gaps.” Before she could stuff the file back under the floorboard, a key rattled in the front door lock.