From 11:00PM PDT on Friday, July 1 until 5:00AM PDT on Saturday, July 2, the Shmoop engineering elves will be making tweaks and improvements to the site. That means Shmoop will be unavailable for use during that time. Thanks for your patience!
Though not exactly a person, the yellow fever epidemic is the main villain in this novel. It's what takes away the people Matilda loves the most, and it's what drives others to do very bad things. The fever also presents the driving conflict that brings out the best in Matilda – the plague forces her to realize just who she is and the strength she is capable of.