Let me take a wild guess. Harry and his pals will be called to adventure. They'll be reluctant at first, but eventually take up the call, pass through some trials, perform supernatural feats, and triumph in the end. Along the way, Harry will learn about himself, develop new abilities or hone existing ones that he didn't realize he was so proficient in. There will be a surprise or two (most likely a central character turning out to be something other than what was first thought). All character and creature types will be borrowed from Tolkein and the plot will be borrowed from Joseph Campbell. Did that ruin it for you? It shouldn't, because every other Harry Potter book followed the exact same formula.