A story that reveals the whole story of a friendship that has been changed over 20 years based on the death of a friend of Jang Jae-kyeong, an ace detective in a drug squad who is forcibly addicted to drugs.

A hilarious royal scheme begins when a fraud pretends to bring back the crown princess with spirit possession.

After summer vacation, So-ri transfers to a new school and finds an anonymous letter in her desk drawer with an introduction to the school and a clue to finding the next letter. While following the clues in the letters and searching all over the school like on a treasure hunt, So-ri keeps running into a same-aged student named Dong-soon. So-ri and Dong-soon quickly become friends as they search for the letters together. As she finds one letter after another, the special connection continues, and So-ri's curiosity grows for the mysterious sender.

A man and woman shaped by loss and time separate in youth, then reunite ten years later to find their once-shared bond still guides them through love, grief, and adulthood.