The Wasp Factory is probably the most detailed literary window into murderous madness I've peered into. The narrator, Frank Cauldhame, admits to having killed two cousins and a brother but claims that he doesn't intend to kill again, as "[i]t was just a stage [he] was going through."
Banks has created a parallel world for sixteen-year-old Frank and his father, Angus; they live on an island, which Frank protects with talismans and divinatory magics he has fashioned out of animals and insects he's killed. Frank's was an unregistered birth, and he was gruesomely injured at a young age, so he only interacts with the outside world when he heads down to the pub for drinks with his only friend, a dwarf. The rest of the time, Frank patrols the island with a satchel full of pipe bombs and dead animal heads. Frank is unsettled by the prospective return of his brother, Eric, who is as mad as Frank but in a more dramatic way (he was institutionalized after burning the village's dogs and trying to force children to eat worms). Eric has escaped and is making his way back to the island, leaving a trail of burnt dogs in his wake.
Frank is deeply introspective, but while he is able to recognize both his brother's and father's mental problems (Angus is obsessive-compulsive at the very least) and the social unacceptability of his murders, only at the end does he seem to obtain some meaningful self-knowledge.
[Spoilers follow; highlight to read.] When the book's final twist manifests itself, I felt a curious softening toward Frank. His previous actions suddenly seemed less of the product of an alien intelligence and more sympathetic. That the book elicited this reaction made me very uncomfortable; I can only assume that it happened because I am a woman, but it strikes me that there's something extremely problematic about suddenly becoming more forgiving of multiple homicide just because it's a fellow XX chromosome carrier who did the deed. There's something deeply at work here with regard to societal views of female killers and internalized stereotypes, and as a self identified feminist it made me feel roughly the same way most believers in racial equality feel after they take one of those implicit association tests and it tells them they're prejudiced. This sudden rush of sympathy for Frank, more than anything else in the novel, unsettled me.
I'd recommend this book to anyone who watches Silence of the Lambs because they like Hannibal Lecter.