Charlotte was a beloved member of the Thornton family, by relatives and townspeople alike. She had a lovely singing voice and cared about everyone, living or dead. Her younger sister Harper looked up to her very much and the two were very close. When their cousin Clara came to live with them in 1973, they welcomed her with open arms and treated her like a sister. However, tragedy struck in 1984 when Charlotte's parents died together in a plane crash, making Charlotte the new head of the Thornton family business. At some point she created a will that left everything to Clara in the event of her death.
On October 30, 1989, the Thornton family threw an 1800's-style masquerade ball for Charlotte's twenty-first birthday. Just after the party ended, the building Charlotte was in caught fire, and she died within its smoke and flames. The entire family was heartbroken. On her tombstone they chose the sad, loving epitaph "Dear Sweet Charlotte, Please Come Back". As rumors started to spread that Charlotte's ghost was haunting Blackrock Island, her epitaph inspired a rhyme children said to scare themselves silly: "Fire so red, night so black, dear, sweet Charlotte, please come back". They would even climb over the fence to Thornton Hall to try and meet Charlotte's ghost. Those that actually did were terrified; a few even went into shock. Paranormal investigator Savannah Woodham interviewed some of these people for research on the book she was writing called The Ghost of Thornton Hall: True Encounters Retold. It was to be a book she would never complete.
When Jessalyn Thornton goes missing in 2013, Wade suspects Charlotte's ghost may have something to do with it. He calls Savannah hoping she'll investigate, but she's too frightened to accept the case and instead calls Nancy Drew to go in her place. As Nancy investigates, she learns about Charlotte's past. Charlotte had taken great care to lock up her bedroom and hide the keys to access different parts of Thornton Hall all over Blackrock Island with complicated puzzles, writing in her journal that she may have been afflicted by that "good old Thornton family paranoia".
However, Nancy eventually finds out that Charlotte did have reason to be afraid. The day before the fire, Charlotte changed her will so that everything would be left to Harper instead of Clara. Somehow, Clara found out that she had been cut out of the will and became scared that it meant she was being cut out of the family entirely. Having already lost her mother, she didn't want to lose the only other family she had left. Her fears caused her to grow angry and she confronted Charlotte about the decision to change the will. Wanting to scare Charlotte a little, Clara started a small fire, but it quickly got out of control and ended up killing Charlotte. Horrorstruck at what she had done, her guilt and grief led her to sit at Charlotte's grave every night for a year. But despite her heartbreak, Clara took the necklace Charlotte was wearing the night of her death, convinced that it held a clue to finding the will. Unfortunately for her, the necklace was an heirloom from their civil-war-spy ancestor, meaning that if the locket was opened incorrectly, it would destroy whatever was inside.
Nancy eventually discovers that all this time, Jessalyn had been working with Harper to get the necklace. Harper had found Jessalyn the night of her bachelorette party and asked for her help in proving that Clara killed Charlotte. Knowing that her mother has always seemed so cold to her, and believing that this dark secret explains this behavior, Jessalyn thinks that this manner of Charlotte's death could be true. She and Harper have been dressing up as Charlotte in order to scare Clara away from her briefcase, where she keeps the necklace. Agreeing to help Jessalyn and Harper, Nancy manages to get the necklace open and recover the will right when Thornton Hall catches fire.
If Nancy decides not to rescue Clara from the flames, a resident of the town tells Nancy that she saw two ghosts float up into the sky like smoke from the ruins of Thornton Hall, implying that the spirits are Clara and her dear cousin Charlotte.
- Jessalyn and Charlotte are said to have very similar personalities. Both are described as the "bright spots of happiness" of the Thornton family.
- Charlotte used to sit inside the crypt to keep her ancestors company, believing that they shouldn't be forgotten.
- It's possible Charlotte's name came from the word "char", which means "to partially burn".