Lucely is a 12-year-old girl living in St. Augustine, Florida, who possesses the rare ability to see her deceased relatives as human-like ghosts rather than the fireflies everyone else sees. She honors her Dominican heritage through language, food, and a deep respect for her elders. Faced with the potential foreclosure of her ancestral home and a mysterious weakness affecting her ghost grandmother, she takes proactive steps to protect her loved ones.

Syd is Lucely's best friend, blending a somewhat dorky personality with an intense fascination for magic and the occult. She willingly jumps into dangerous situations, offering rule-breaking solutions to help Lucely's family keep their house. Her knowledge of historical spells proves vital as the girls begin investigating the town's hidden past.

Babette is Syd’s grandmother and the proprietor of Babette's Baubles, a secluded shop filled with potions, strange artifacts, and books. She maintains a no-nonsense presence and clearly understands more about the supernatural world than she initially shares. She lives in a confusing, magically inclined house protected by a lake and several unusual cats.

Simon is Lucely's father and an enthusiastic history geek who runs a local ghost tour in St. Augustine. Still mourning his departed wife, he has lost the ability to see the family ghosts in human form, perceiving them only as ordinary fireflies. He struggles financially with his tour business and faces the heavy burden of potentially losing the family's ancestral home.

Eliza Braggs is a historical colonist from St. Augustine's past. According to local lore, she harbored an intense, irrational hatred for the Purple Coven witches and successfully organized a mob to have them executed and exiled. Her legacy of prejudice and violence continues to haunt the town's magical history.

Mamá Teresa is Lucely's deceased grandmother and the respected matriarch of the Luna family ghosts. She usually provides comfort and wisdom to Lucely, but recently falls victim to a mysterious weakness that drains her energy. Her declining state motivates Lucely to seek out a supernatural cure.

Tía Milagros is Lucely's deceased aunt, permanently appearing in the hair curlers, pajamas, and sleep mask she wore when she passed away. She frequently pesters the family about chores and gossips about the neighbors. Despite her bossy exterior, she genuinely loves her niece and the rest of the family.

Manny is Lucely's teenage cousin who died ten years ago. He is a hip ghost who begins experiencing frightening visions and memory loss as a dark energy approaches St. Augustine. He actively warns Lucely about the impending danger.

Macarena is a youthful and strong ghost cousin who acts like an older sister to Lucely. She retains a significant amount of spiritual energy and actively assists Lucely and Syd when they encounter dangerous situations during their graveyard explorations.

Frankie is a deceased cousin of the Luna family who was a highly successful boxer during her life. She maintains her fighting spirit in the afterlife and willingly uses her physical prowess to protect Lucely from aggressive entities.

Mayor Anderson is the tall, mustachioed mayor of St. Augustine. He begins behaving erratically, sneaking around local cemeteries at night. Lucely and Syd catch him on tape discussing a sinister plot to collect souls and take over the city on Halloween.

The Purple Coven, or Las Brujas Moradas, is a historical group of witches who settled in St. Augustine. They served the locals and protected the town from malicious spirits until they were targeted by a witch hunt. Legend states they buried a book of spells before being driven out of the city.

Mr. Vincent is a bank representative who dresses in shiny suits. He arrives at the Luna residence to deliver the bad news that the bank will foreclose on their property if Simon cannot make his payments within the month.

Chunk is one of the many mysterious cats living at Babette's Baubles. She is unusually perceptive and seems to act as an alarm system for Babette, howling to prevent the girls from snooping, but also accompanying them on late-night cemetery runs.