Miranda Priestly is the high-powered, well-feared editor-in-chief of Runway magazine. She rules the fashion industry with a glowering disapproval, churning through assistants at a record speed. (She is portrayed by Meryl Streep).

This is the story of the professional adventure of Andrea, whose greatest dream is to become a journalist. Andrea gets a job in the fashion industry through Runway magazine, the most famous of its type, in order to gain useful experience and contacts to help her writing career. It soon transpires that Andrea won't develop her writing skills in the magazine, instead showing an unexpected talent as the editor in chief's (Miranda) assistant. Miranda is a merciless, sophisticated and cruel woman, making the experience of being her assistant a living hell for every applicant. The working environment is cold and extremely critical, with physical appearance being more highly valued than talent or ability. Andrea realises she will have to change her simple and plain style for a more fashion-aware and elegant one, in order to gain the acceptance of her ruthless boss and colleagues, specially Emily, her unpleasant workmate. Andrea has an epiphany when she realises that she is expecting to take away experience and contacts from the job while giving nothing in return. As a gesture to Miranda she drastically changes her clothes and self-image, with the help of Nigel, the magazine's art director. Nevertheless, the job becomes extremely demanding, because of Miranda's tough work routine and nearly impossible tasks, leaving Andrea without a private life with her boyfriend, family and friends. Maybe the old Andrea has gone, now more preoccupied about her image and her future in the magazine.

As Andrea becomes more immersed in her new life she is slowly losing her old one. She goes to Paris with Miranda for fashion week, and starts to lose herself completely in the fashion cocoon. When she discovers that Miranda is about to be replaced as editor in chief of Runway, Andrea frantically tries to warn her. The moment of clarity for Andrea comes when she realises that Miranda has sacrificed the career (and friendship) of Nigel in order to protect her own position as editor. During a car journey with Miranda, Andrea realises she is turning into Miranda and she is horrified. When Miranda is enveloped by paparazzi when the car stops, Andrea takes the opportunity to literally walk away from it all, hurling her cell phone (a symbol of her servitude) into a fountain.

Miranda Priestly’s daughters are the 11-year-old twin girls, Caroline and Cassidy Priestly, in The Devil Wears Prada. They primarily serve as a demanding, high-maintenance force in the story, famously tasking Andy Sachs (Anne Hathaway) with getting unpublished Harry Potter manuscripts. In the 2006 film, the twins were portrayed by real-life twin actresses Colleen and Suzanne Dengel. While their characters are primarily present to highlight their mother's demanding professional life and busy schedule, they resurface as central figures in the film's sequel, where Miranda enlists Andy's help to manage them as they grow older.