The Mirror is the story of Shay Garrett and Brandy McCabe Maddon, granddaughter and grandmother, who switch times and bodies when they are twenty years old through the Wedding Mirror. Shay is transported into Brandy's body the night before her wedding to Corbin Strock and Brandy is transported into Shay's body the night before her wedding to Marek Weir. Shay, in Brandy's body, is considered mentally unstable and Corbin Strock marries her to get control of the Brandy Wine Mine. Shay befriends Thora K, Corbin's mother, and she continues to live with her even after Corbin's death. Shay marries Hutch Maddon, the man she recognizes as her grandfather from Bran's wedding photo, and they move onto a ranch. Shay is happy with Hutch and her family comes to regard her predictions as a part of life.

Shay gives birth to her own mother, Rachael, and makes sure her father Jerry is taken care of as a child. Rachael grows up revering the Gingerbread House, feeling something is missing from her relationship with her mother. After Hutch dies, Shay travels the world in Brandy's body. All of her predictions for Rachael come true, including Rachael's career as a writer and her marriage to Jerry Garrett. Brandy finds herself lost in Shay's body, in a world that moves at a much faster pace than her own. Grandma Bran dies the very night before Shay is supposed to get married, and Brandy finds herself attending her own funeral. She is attracted to and afraid of Marek Weir, and startled to discover that Shay is pregnant. Rachael and Jerry's marriage has deteriorated, and they are basically staying together for Shay. Marek feels that Shay is an entirely new person, and he feels protective of her. Brandy runs away from the Gingerbread House when Rachael and Jerry discuss abortion, and she is carried by Shay to the home of Mr. St. John. He cares for Brandy and for Shay's growing pregnancy, though Shay's family and Marek think she may be dead.

Mr. St. John's granddaughter Lottie finally reveals Brandy's true whereabouts to her family, and she and her twin sons are taken to Nederland to live in Jerry's cabin. Rachael reads her mother's old diary and discovers the truth: that Shay and Brandy switched bodies. The Gingerbread House is broken into and the mirror stolen. Marek eventually commits to Brandy and the children, with full knowledge that the woman he loves is Brandy McCabe and not Shay Garrett. The mirror continues on its path of destruction en route to New York City.