After her mother Liu Xiuying dies following a terminal illness, a grieving Xu Xingyue finds a strange door inside her family home. Stepping through it lands her in 1980, face to face with her nineteen-year-old mother studying for the national college entrance exam. Knowing that her mother's deepest regret was never making it to university, Xingyue sets out to rewrite that history, matching wits with her own grandfather Liu Jianguo and turning modern study methods on the past.
