A young woman working in a New York restaurant discovers a handbag left on the subway and returns it to its owner, an elegant but lonely French widow named Greta. The two strike up an unlikely friendship, but it soon becomes clear that Greta has a disturbing obsession with cultivating vulnerable young women, and she refuses to let go when her new companion tries to distance herself. What begins as a psychological thriller escalates into something far more dangerous as Greta's controlling behaviour turns sinister.