Primarily books with pumpkins on the covers, or pumpkins in the title. A few where pumpkins are actually characters in the plot.
Most, if not all, of these will also work for the Halloween Square.
Any recommendations, please add in the comments and I'll get them on the list asap.
1.
by William L. Hedges, Washington Irving
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4.
by Walter Scott, William F. Nolan, E. Nesbit, Peter Straub, Tina Rath, John Shirley, Charles de Lint, Esther M. Friesner, Gary A. Braunbeck, Caitlín R. Kiernan, Norman Partridge, F. Paul Wilson, Nina Kiriki Hoffman, Peter Crowther, Joe R. Lansdale, Chelsea Quinn Yarbro, Ste
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7.
by Heather Vogel Frederick
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21.
by Constance Barker, Jim DeBellis
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25.
by J.K. Rowling, Mary GrandPré
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Murder by Death
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FWIW, there's also "Trick or Treat: A Peanuts Halloween" (ISBN 13: 9780345464132; ISBN 10: 0345464133) -- and both Peanuts books would also work as comic relief for "Set on Halloween."
As for horror books, I haven't read either of the below, but judging by the covers / descriptions, they would fit:
R.L. Stine: "Halloween Night" (ISBN 10: 0590460986; ISBN 13: 9780590460989) and "Attack of the Jack O'Lanterns" (ISBN 10: 059056885X; ISBN 13: 9780590568852) -- both likewise for "Set on Halloween," of course.
I added the books, and I also edited the description of the list to say that most of these, if not all of them, would also qualify for Halloween. Seemed more expedient. :)
The Danger, by Dick Francis.