Lan Tianyuan is a nine-year-old boy who lives with his grandmother in a village at the foot of the mountains. His parents went to work in the city to offer the family a better life. As grandma's birthday is coming up soon, Tianyuan wants to buy her a cake. But, in order to make this surprise, he has to go to the city. Without saying anything to his grandmother, he digs under a tree for his "treasure" (money that he had saved on different occasions), puts a few things in his bag and leaves in a hurry on mountain roads to reach the nearest train station, located two hours away. He arrives at the station, but he missed the train... And yet, he must get to the city. His road will be strewn with many adventures, and once he reaches the city, things get complicated, taking an unexpected turn.
Will Tianyuan be able to manage alone in the big city? Will he be able to face the difficult situations he will face?