In simple terms, Autumn is about the relationship that develops between a 9-year-old girl called Elisabeth, and her elderly next door neighbour, Daniel Gluck. There's a lot more to it than that tho'.
It's a book firmly set in its time, that of the UK post-Brexit. Lack of funds for community services have led to libraries being closed, the way the Brexit referendum was framed has led to thoughtless tribalism, and the idea of protecting the land from invasion by foreigners is rife.
The style of writing won't be to everyone's taste. Its story structure doesn't begin at the beginning, nor does it end at the ending. The narrative moves back and forth, a bit like how your mind flits around when you're staring into space, not thinking of anything in particular. Or like a jigsaw puzzle; two pieces side by side seem unconnected, but after a while you come across an image that fits with one you saw, or read, earlier.
If you're a reader who likes to investigate references within the story, Ali Smith provides a wealth of google-worthy material: the Profumo scandal, female pop-artist Pauline Boty, quotes from Dickens's A Tale of Two Cities.
Don't be put off tho'. There's plenty of humour and warmth. An early scene in the post office made me smile, recognizing the petty bureaucracy of the man behind the counter. Elisabeth's mother's act of vandalism brought a cheer and a laugh in the way she sticks it to authority. But above all, the humanity of the relationship between Elisabeth and Daniel gives us hope for the future.