One day, Lan Xia goes to her classmate Hai Feng’s house to stay overnight. They start to feel awkward around each other without really knowing why, but slowly get closer through insignificant words exchanged while doing a jigsaw puzzle of the world map. The next morning, Hai Feng realizes that Lan Xia has left without saying anything and sets out to follow her. A memory of a summer in which the world belonged to the two of them alone, if only for a moment