94-year-old Eleanor Morgenstein tries to rebuild her life after the death of her best friend. As a result, she moves back to New York City after living in Florida for decades.
Federal agent Alexandra Barnes believes that Catherine Petersen is a serial killer who marries rich men and then murders them for their money. But since Catherine is seemingly a master of disguise and has multiple identities, Alexandra can't prove anything with conventional detective work. With no other option, she goes undercover, pursuing the same man as Catherine, and hoping that Catherine will slip up and reveal her true identity.