Eloise "Ellie" Turner, a sweet and naive teenager with troubled mental health, loves the music and fashion of the Swinging Sixties and dreams of becoming a fashion designer. Her mother, also a fashion designer, killed herself in her childhood, so Ellie was raised by her maternal grandmother. She occasionally sees her mother's ghost in mirrors, something her grandmother is aware of.
Ellie moves from her rural home near Redruth, Cornwall to London to study at the London College of Fashion, where she has trouble fitting in with her peers, especially her bullying roommate Jocasta. Only John, another student, is kind to her. Unhappy in the dormitory, she moves into a bedsit owned by the elderly Ms. Collins.
That night, Ellie has a vivid dream where she is transported back to the 1960s. At the Café de Paris, she observes a confident young blonde woman, Sandie, inquire about becoming a singer at the club. Sandie begins a relationship with the charming Mod manager, Jack. The next morning, Ellie designs a dress inspired by Sandie and discovers a love bite on her neck.
Ellie has another dream in which Sandie auditions at a Soho nightclub, arranged by Jack, before returning to the same bedsit that Ellie has rented. Inspired by these visions, Ellie dyes her hair blonde, changes her fashion style to match Sandie's, and gets a job at a pub. She is observed by a silver-haired man who recognises her similarities to Sandie. In further dreams, Ellie discovers Sandie is not living the life she had hoped for, now being pimped by Jack to his male business associates.
Panicked, Ellie goes to inform Ms. Collins that she is leaving London. Ms. Collins tells her she knows she went to the police because the "nice police lady" came to check up on her. She then reveals that she is Sandie. Ellie's vision of Sandie's death was actually a vision of Sandie killing Jack when he threatened her with a knife. Sandie then lured the men she was pimped to back to her room and killed them, hiding their bodies in the house's floorboards and walls. Ms. Collins has drugged Ellie's tea with the intention of killing her to ensure her silence.
In the ensuing scuffle, Ellie knocks over an ashtray and starts a fire. John comes to Ellie's aid, but Ms. Collins stabs him and continues after Ellie, who hallucinates Ms. Collins as the younger Sandie, and that they are ascending a glass staircase. Ellie kicks Ms. Collins, sending her down the stairs. She flees to her room, where the spirits of Sandie's victims plead with her to avenge them, but she refuses. Ms. Collins enters Ellie's room, where she also sees the spirits and is struck by "Jack". With the police outside, she attempts suicide but Ellie stops her, understanding why she did what she did. Sandie tells Ellie to save John and herself, remaining in the building as it burns.
Ellie enjoys success as her designs are showcased at her end-of-year fashion show and is congratulated by her grandmother and John. Ellie sees her mother and a vision of Sandie in a mirror. Her mother smiles at her and Sandie blows her a kiss.
