Frances (Chloë Grace Moretz) is a sweet, naïve young woman trying to make it on her own in New York City. Having recently lost her mother to cancer, she maintains a strained relationship with her workaholic father. One day, Frances finds a handbag on the subway and promptly returns it to Greta (Isabelle Huppert), an eccentric French piano teacher who loves tea and classical music. Frances quickly grows closer to widowed Greta and the two become fast friends. But when Greta's behavior becomes increasingly erratic and obsessive, Frances does whatever it takes to end the toxic relationship before things spiral out of control.