Cassandra "Cassie" Nightingale is a mysterious, darkly beautiful woman. She moves into an old, abandoned house which is reputed to be haunted by its original owner, "The Grey Lady". The small community is divided in their opinion of her: Some want her to stay (especially widowed police chief Jake Russell and his two children), while others want her to leave. Through the course of the story, seemingly magical things happen, and the community attributes these occurrences to her. Everyone begins to wonder if she is really a witch.
She owns and runs Bell, Book & Candle, a shop in Middleton as well as Grey House. She was previously married to Jake Russell, the police chief of Middleton. Jake had two kids from his previous marriage, and he and Cassie had a child together, Grace.

After Jake’s untimely death, it took Cassie years before she decided to open up her heart and begin dating again. She eventually began dating Dr. Sam Radford, after he moved to town. They dated several years before marrying in season 5.