Harry and Doug are ready to rule the third grade-- if these two best friends can find the right room! But third grade turns out to be a whole new adventure, with a different classroom and new teachers. Some things never change, though, and Sidney La Fleur is still Horrible Harry's sworn enemy. On the first day, Sidney kills the pet spider that Harry brought in for show-and-tell, and Harry vows to get even. When Miss Mackle announces the class trip to the Old New-Gate Prison and Copper Mine, it seems like the perfect chance for Horrible Harry to get revenge. What will happen? And how can Doug visit the copper mine when he's scared stiff of going underground?