[sun surfer]

My very quick initial idea is something tied to the time of year since I don't think we've ever done anything like that for this time of year.

Maybe a topic related to Halloween such as 'All Hallows' Eve' or 'Samhain'. This could be a book set around Halloween (or any of its prior incarnations or various culturual incarnations) or having to do with something related to Halloween, such as horror, magic, cemeteries, ancient rituals, witches, ghosts, werewolves, vampires, etc. While it may sound like a more directed topic, I could definitely see some interesting interpretations that go in varying directions.

If we wanted something more general but still about the time of year, maybe we could do 'Autumn' and have it related to the season. I do realise it's spring in the southern hemisphere though which could complicate things! We could do 'Autumn & Spring' (or 'Spring & Autumn'!) and have it be books related to one of the two seasons, and I think it still works as a cohesive topic since these two seasons are about change and movement. Alternately, if we are okay sticking closer to autumn, we could do 'The Fall' which would open up the topic to multiple other interpretations since 'fall' could mean so many things and 'the fall' in particular can conjure up ideas of someone or some group having a collapse in some way. Or maybe that's just fresh in my mind since I not too long ago finished up the television series of The Fall in which each episode's name is a line from Milton's Paradise Lost.