GK Chesterton's Orthodoxy includes an early section The Maniac which impressed me greatly from the first time I read it. If you have never read Chesterton, this would be an excellent place to let him introduce himself. It captures wonderfully his ability to take conventional wisdom and platitudes and see that they are not merely banal, but 180 degrees wrong. The first paragraph alone should hook you, and is a superior introduction to my discussion than anything I could write myself.
For the unfamiliar early 1900's references, Hanwell was an insane asylum outside London, a companion to Colney Hatch mentioned in The Magician's Nephew. Joanna Southcote was a self-proclaimed prophetess (c. 1800) who declared she was the woman spoken of in Revelation 12 and would give birth to the Messiah at age 60. Even after her death, she had followers in England for many years.