Halloween has always had a significance in the Harry Potter series. To start with, it’s the date of lexicon.org/event/defeat-of-voldemort-james-and-lily-potter-are-killed/">James’ and Lily’s deaths and Voldemort’s downfall in 1981. Then, in Philosopher’s Stone lexicon.org/character/quirinus-quirrell/">Quirrell tries to take the lexicon.org/thing/philosophers-stone/">Stone for the first time by letting the lexicon.org/creature/large-magical-beasts/trolls/">troll in; in Chamber of Secrets the chamber is opened and lexicon.org/character/mrs-norris/">Mrs Norris is Petrified; in Prisoner of Azkaban, Sirius breaks into Hogwarts and attacks the lexicon.org/character/fat-lady/">Fat Lady; and in Goblet of Fire, Harry’s name comes out of the lexicon.org/thing/goblet-of-fire/">Goblet. All of these events are major plot points in their respective books. You could even say they are all the beginning of the main plots – they all involve the titles of their book: the Stone, the Chamber, the Prisoner and the Goblet. Why do things stop happening on Halloween after that? There’s no mention of Halloween in the last three books. It might just be because it was starting to seem a bit too coincidental. Possibly more to the point, why have so many significant things happened on Halloween – is it just coincidence; is it dramatic licence; or is there a genuine magical reason for it? According to legend, Halloween is the day of the year when the veils between the physical and spirit worlds are at their thinnest – when magic is most active. Is it possible that this is true in the wizarding world, and there could be particular power associated with performing magical acts on Halloween, similar to the power associated with the number seven? Admittedly it’s hard to make this connection with the events in book three – even if Sirius does know it’s Halloween, it seems more likely he chose that day just because he knows Gryffindor Tower will be empty, rather than to give him enhanced magical power. But even if this occasion is coincidence, that doesn’t mean all of them are. It could account for the first three events, which all involve Voldemort; if it’s true, he would definitely want to perform the acts of defeating his would-be enemy and creating a lexicon.org/thing/horcrux/">Horcrux from his death, rebirthing himself using the Philosopher’s Stone, and reopening the Chamber of Secrets in the most powerful way possible. (Interestingly Halloween is also associated with divination and death, which makes it an even more fitting day for Voldemort’s attack on the Potters.) And perhaps the Goblet of Fire only works, or works best, around Halloween, somehow drawing more power from the heightened magic in the air. But if we accept this is true, it raises a different question – why don’t more things happen on Halloween? Why doesn’t everyone do everything of magical importance on this day of the year, especially Voldemort? I would say because logistically it simply doesn’t make sense: if you’re ready to do something like create a Horcrux in say springtime, it would be a pain to wait half a year and then do everything on one day. But if you’re planning on doing it around autumn time anyway – like the four events I mentioned earlier, excluding Sirius – then it makes sense to plan it on Halloween. There’s no evidence for any of this, but it goes a way to explaining this repeating coincidence. Let us know if you have any other thoughts or explanations!