Madness in Iain Banks' "The Wasp Factory" is double-layered. The adolescent narrator has a clear developing psychopathy as a triple murderer and lover of animal brutality, with elements of psychosis; his brother is already locked away following a gruesome trauma.  A tense thriller that is entirely realistic, if frightening, in its execution.  

20 – “My dead sentries, those extensions of me which come under my power through the simple but ultimate surrender of death, sensed nothing to harm me or the island” 

41-2 – “The death of someone close to you gives you a good excuse to go a bit crazy for a while and do things that would otherwise be inexcusable.  What a delight to behave really badly and still get loads of sympathy.

[...] That’s my score to date.  Three.  I haven’t killed anybody for years, and I don’t intend to ever again.  It was just a stage I was going through.”