A Shadow over the Chateau (1960)

Zhou Mengdan and her fiancé Chen Luhua visit her aunt, Madam Chen, where Luhua unexpectedly reunites with Madam Chen's adopted daughter, Li Ke'er. Madam Chen suddenly passes away, which raises suspicions for Mengdan. Coupled with a falling out with Luhua, Mengdan moves in with Li Ke'er, only to find her daughter has died from poisoning, making Mengdan a suspect. Luhua's friend, Dr. Luo, investigates the case and, together with a private investigator, eventually uncovers the true culprit.