The Eye of the Beholder by Marc Behm
'One of the punchiest, bleakest, weirdest hard-boiled crime novels I've ever come across, and one of the most original. This slender novel covers 30 years and details over 100 killings. It's a picaresque-epic thriller, a nihilistic road movie: Sam Spade meets Badlands. Vicious episodes occur in almost every section of the country, and the back and forth travel patterns weave a web across the USA. Behm's Eye is a voyeuristic near-sociopath who spends three decades dogging the footsteps of a bi-sexual serial murderess who, in a chameleon-like series of disguises, wanders the country acquiring then snuffing out one well-heeled partner after another. The Eye of the Beholder is a private-eye novel to end all private-eye novels' - Los Angeles Herald Examiner