Andy Sachs, an aspiring journalist, lands a job as the assistant to Miranda Priestly, the powerful and ruthless editor-in-chief of Runway magazine. Despite having little interest in fashion, Andy struggles to adapt to the cutthroat world of high fashion where she's expected to cater to Miranda's every whim. The working conditions are grueling, with Miranda demanding perfection and willing to dismiss anyone who doesn't meet her expectations. Andy is initially overwhelmed and considered an outsider by her fashion-savvy colleagues, especially Miranda's senior assistant, Emily. To keep up with the relentless pace, Andy decides to overhaul her wardrobe and attitude with the help of Nigel, the magazine’s art director.

As Andy continues to excel in her role, she faces growing tension in her personal life, particularly with her boyfriend Nate, who feels neglected due to her demanding job. This transformation in Andy causes a rift in her relationships and pushes her to question her own priorities and beliefs. While trying to balance the pressure from Miranda's impossible demands and the personal sacrifices she has to make, Andy gains insight into the reality of the fashion industry and the cost of success.