When Kim Sin-yeol’s husband, Kim Sung-do, passed away in October of 2017, she became the sole resident of a remote island between Korea and Japan. The claim to this territory has been under dispute for centuries. While organizing some of her late husband's belongings, Kim Sin-yeol discovered a mysterious locked box. Kim Sung-do loved puzzles and would always set up scavenger hunts for his wife around the island. The top of the box had a note that read, “As my final gift to you, my love, I’ve setup one final test of your wits, can you open the box?”