Fairy stone
In order to summon her incubus to then tell him to leave Callie uses her fairy stone her father gave to her when she was younger. She later uses it to make an ice ornament with Brock, and he tells her that sometimes giving something away gives it more power. The stone later comes back to her when she needs it the most, to save her life at the end so there is truth to those words. Callie uses to stone to draw power, to draw strength from it in the time of need. It represents her bond to her parents and to what she truly is.
Names
It is clear that names of characters and places are no coincidence. Fairwick is the most obvious example as a name of a place where fairies and witches and those alike mix together. Callie's last name McFay alludes to her true nature. Fiona Eldritch is the queen of fairies and the actual word eldritch is used to describe something otherworldly. Even the name Anton Volkov is an expected, not to say a cliché, name for a vampire.
Writing
Callie is a writer herself, who wrote a book, inspired by her own experiences, about demons. The house she moves in previously belonged to a famous writer who wrote Gothic fiction inspired by her own dreams, disturbingly close to Callie's. The novel itself is a Gothic fiction therefore there is an element of Metafiction embossed in here.
Dreams
Dreams are, by one definition, representations of one's most inner desires or fears. This notion of dreams is used in here as well. Callie's dreams about her demon lover are her inner desires, the ones which she can't achieve in her daily life.
