One might think I would hardly have to describe Dr. Jekyll and Mr. Hyde, by Robert Louis Stevenson. It's been done so often in the movies that pretty much everybody knows the concept. Yet, I think the book itself is probably not read very often, so I'll just give a quick rundown.
The lawyer Mr. Utterson is troubled by a will he has made for his friend Dr. Jekyll. The will provides for a certain Mr. Hyde to take over Dr. Jekyll's entire estate in the event Jekyll is missing for more than three months. Mr. Utterson is afraid that this Mr. Hyde has some sort of blackmail material on Dr. Jekyll, and his fears are intensified when another acquaintance tells him a horrible story about Mr. Hyde. The friend himself witnessed Mr. Hyde stomp directly over a young girl on the sidewalk, and only when the friend and the girl's family confronted and threaten him did Mr. Hyde attempt to make restitution--by providing the family with a check signed by Dr. Jekyll.
The more Mr. Utterson investigates, the more troubling the case becomes. It seems Jekyll and Hyde have a close relationship--but what can the well-known surgeon Jekyll have in common with a street thug like Hyde? After Hyde is implicated in a murder, and Jekyll disappears, Utterson and Jekyll's loyal butler, Mr. Poole, break down the door to Jekyll's lab and learn the awful truth.
One thing that struck me about the book is that it is not clear whether Mr. Hyde has a different personality from Dr. Jekyll, or simply a different body, allowing Dr. Jekyll to carry out behaviors he's always longed to do. According to Dr. Jekyll, Hyde isn't held back by the feelings of conscience that restrict Jekyll from acting on his basest impulses. Yet, Jekyll also admits that he has long has terrible urges and even acted on them from time to time, though never enough to satisfy him because full indulgence would cost him his reputation. (These urges are never really specified, though apparently Nabokov thought they must be homosexual in nature. That's an appealing idea, but I don't know how well it fits, because the crimes we do see Hyde engage in are crimes of violence.) It's clear we can't really trust Jekyll's account of himself. Thus it remains ambiguous whether Hyde is truly a separate persona, or merely Jekyll with a foolproof disguise.
The book is so short and easy to read, and such a touchstone in our culture, that I'm going to make up a new category for it called No Excuse books, joining my existing Shortcuts to Smartness book category. These are short but important books that no educated adult has an excuse not to have read, except they haven't gotten to it yet. (I'm also going to retrospectively add the Epic of Gilgamesh to this category.) It's also fun to read! It's a tense story with true horror elements. I'm not sure what took me so long to get to it, and I highly recommend it.