In an unspecified time when epidemics run rampant, botanist Yan Guo and his fiance-assistant Baobao move to Moon Island, a nature reserve, to research the curing properties of rare plants. As is customary, they pray to the magical Eros Tree to cement their love, unaware that they have to undergo a severe trial, in which Baobao must remain unseen to Yan for three years in exchange for his life.