Lan Tianyuan lived with his grandma in the mountains since his parents were working in the city. When Grandma's birthday was coming, he decided to buy a cake for her.He went to the city secretly and found the life there was different from his. With all difficulties, he finally came back with the cake.During his journey, he met with different people, some were good but some were not. He found he has learned a lot from this short but magic journey.

《奶奶的蛋糕》是张菱儿的中篇小说。作者关注农村留守儿童，讲述了蓝天远为了给奶奶庆祝生日，第一次踏出山区买蛋糕的故事。在旅程中，他遇到好心人也遇到过坏人，在短短的旅途中，收获了见识和成长。