Three years ago, her younger brother vanished. From photos, from records, and from everyone's memory. Han Seo-yun, a lost-and-found clerk, has been the only one keeping a record of her forgotten brother, Han Yu-jun. One night, a week before the lost and found is set to close, she discovers her brother's worn yellow umbrella on the disposal list. When she opens it, rain falls only beneath it, and her brother's handwriting surfaces on the wet fabric. "Sis. Don't look for me. There are still people here." But the one who returns through the door the umbrella opened isn't her brother. There are four chances to bring people back, and five who need to return. Every person she saves narrows her path to her brother. Following the traces left on objects and the records that were erased, Seo-yun begins searching for a way to leave no one forgotten.