In the spirit of the spooky season, this episode is all about spirits and specters in the wizarding world.

Emily and Katy, who recently published a new article titled "Harry Potter and Historical Witness: The Pensieve and the Time-Turner," are joined by Louise Freeman, fresh off our two-part episode on memory, and David Martin, member of the winning Hufflepuff team on Harry Potter: Hogwarts Tournament of Houses and author of Twelve Fail-Safe Ways to Charm Witches and Other Thoughts About Harry Potter.

Why does Hogwarts have ghosts? David thinks that ghosts are representations of the past and the influence of the past on the present, so a thousand-year-old castle is bound to be full of history. Louise sees the influence of Gothic novels, in which old castles tend to be haunted.

We debate the dynamics governing ghosts and their interactions with the world around them. Ghosts don't age, but can they evolve emotionally? Peeves is a different kind of spirit altogether as a poltergeist and can interact with objects in a way the Hogwarts ghosts cannot - and thus cause much more chaos. Ghosts are also distinct from the form of Tom Riddle that emerges from the diary, the figures that appear with the use of the Resurrection Stone, and Voldemort's victims conjured by Priori Incantatem.

Most of the ghosts at Hogwarts lived centuries ago. Why did they choose to become ghosts and stay at Hogwarts? In addition to a fear of death, we discuss what unfinished business they had on earth - which could be coming to terms with death. Once ghosts finish their business, can they ever move on?