My favourite autumn novel is Dragonfly by Frederic S. Durbin - it is about a 10-year-old girl nicknamed "Dragonfly" who gets transported to the land of Harvest Moon, which is ruled by the evil despot Samuel Hain. This book has the very best opening paragraph I've ever read, and it hooked me immediately:
"Bad things were starting to happen again in Uncle Henry's basement. These were things that had happened before, when the wind swung round, when the trees all felt the blood rush to their leaves after the exertion of August and the idling of September; when the chuckle-dark harvest moon shaped pumpkins in its own image, brought its secret wine flush to the scarecrows' cheeks; when the rich bounties of the land lay plump for the taking and the light left them alone for longer and longer at a time. But when the trouble started before, I was too young to remember."
Another great seasonal read is the Diaries of the Family Dracul trilogy by Jean Kalogridis. This is a prequel trilogy to Bram Stoker's Dracula; the first book starts out a generation before the events of Stoker's novel and last book is contemporaneous with Dracula, but told from a different viewpoint. The trilogy answers many questions left open in Stoker's novel, including the origin of the enigmatic Dr. Van Helsing. This series is a "must-read" for any Dracula fan.