The main characters in The Haunting of Cassie Palmer are almost all members of the Palmer family: Cassie, her mother, and her siblings, Tom and Mary. However, Deverill, the spirit Cassie befriends, plays an important part in the family's affairs.

Although Cassie initially sees herself as "spineless," she is actually a rather headstrong young lady who is not easily intimidated. When abandoned in the dark cemetery, she overcomes her fear by directing her anger towards Tom and Mary. This enables her to complete her "mission" which results in the appearance of Deverill. An independent thinker, she has difficulty reconciling her own ambitions with those her mother has for her. She is careful to avoid hurting her parent's feelings but feels betrayed when "Mum's" shortcomings are revealed—especially when Mrs. Palmer attempts to cover up her own deceit. Yet, Cassie is not without compassion...