A Guide to Medieval Sorcery is a book about magic in Medieval times. It is one of the books Harry Potter consults before the second task of the Triwizard Tournament, hoping to find a way to breathe underwater. He takes this book, along with Madcap Magic for Wacky Warlocks, An Anthology of Eighteenth Century Charms, Dreadful Denizens of the Deep and Powers You Never Knew You Had and What To Do With Them Now You've Wised Up, to Gryffindor Tower after Madam Pince kicks him out of the library on the eve of the task