At a mid-1950s press conference, scenes from an upcoming film star Nina, a beloved screen icon. While on her way to the event, she glances into an ornate mirror, and a vivid flashback carries her back to Rome when she was nineteen. Her cousin Valentina has arranged for her to take a job as a chambermaid in a dilapidated hotel.
In the old city, Nina encounters the aging Signora Contessa Sanziani, once the toast of Europe. The Contessa receives a visit from her husband, Count Sanziani, from whom she has been estranged for forty years. Their quarrels are revived, and the Count leaves with a blunt warning that he does not want to be told if anything happens to his wife.
The Contessa decides to take Nina under her wing and transform her into a polished European figure. One evening, she summons Nina to her room and unveils a sari given by an Indian ambassador; she makes Nina undress, drapes the sari on her, then gives her a haircut and makeup. The transformation is dramatic, and the young woman begins to imagine the Contessa’s life, while the Contessa’s vivid stories echo in her mind. This sparks a series of fantasy sequences, unfolding in lavish casinos and Venetian palazzos, illustrating Nina’s rising ambitions and the allure of a glamorous, world-worn past.
On a rare day off, Nina explores Rome and senses a bright future ahead. That evening, while performing a task for the Contessa, the latter suffers a mental breakdown, and the hotel manager insists she depart the premises. Feeling the weight of the Contessa’s troubles, Nina seeks help from Mario Morello, a frustrated screenwriter who lives in the hotel, hoping he can unravel the Contessa’s old stock certificates Nina has brought with her.
Mario informs her that most certificates are worthless, but he notes that one—issued by the Bank of Congo—might be valuable enough to cover the Contessa’s hotel bill for weeks. With part of this money, Nina helps pay the hotel’s expenses. Later, at a restaurant, a screen director, Antonio Vicari, spots her and, using Mario who is drafting a screenplay for him, arranges a screen test.
Before she heads to the studio, the Contessa has checked out to search for an old flame, Gabriele d'Orazio. In her agitated rush, she is struck by a car and taken to a Catholic charity hospital.
Meanwhile, Nina wrestles with the screen test, but Mario’s guidance helps her speak about the Contessa with genuine feeling, and Vicari decides he wants her in his next film. Nina and Mario later locate the hospital where the Contessa rests under the care of Sister Pia. The Contessa dies soon after, and Nina, moved by the loss, takes the Contessa’s ornate mirror as a keepsake and leaves the hospital.
Back in the present, Nina has become a motion picture star. She arrives at the press conference, and as she steps from her limousine, a young girl hurries up, declaring she wants to be just like Nina when she grows up.