What is youth? It is the warm sunshine shining in an empty classroom, our crazy squandering, our infatuation with a person who hesitates to move forward, or our making promises under the setting sun that can never be fulfilled. Su Mianshu, Shen Liuyun, Liu Yu, Feng Guomei, four girls with very different personalities left behind a string of hidden treasures in their past at the end of their youth, including secret love, madness, loneliness, dreams, and squandering.