Everything seems to be going great... until we notice that there’s still a third of the book left. That means something bad is about to happen.
It's the day of Jane and Rochester's wedding. It should be the happiest day of Jane's life, but during the church ceremony two men show up claiming that Rochester is already married. Dum dum dummm. Rochester admits that he is married to another woman, but tries to justify his attempt to marry Jane by taking them all to see his wife.
Mrs. Rochester is Bertha Mason, the "madwoman in the attic" who tried to burn Rochester to death in his bed, stabbed and bit her own brother (Richard Mason), and who’s been doing other creepy things at night. Rochester was tricked into marrying Bertha fifteen years ago in Jamaica by his father, who wanted him to marry for money and didn't tell him that insanity ran in Bertha’s family. Rochester tried to live with Bertha as husband and wife, but she was too horrible, so he locked her up at Thornfield with a nursemaid, Grace Poole.