3.5; The Eyes of Laura Mars by way of Repulsion; suffers somewhat from a twist that's become nigh-ubiquitous since publication, and the psychosexual motivations get more than a titch questionable, but genuine giallo-type novels in english are all too rare, and the author captures the inside of a broken psyche with an authentic unheimlichness that is often genuinely oneiric.
Really fun if slightly schlocky horror. Captures the feeling of all those classic slasher movies the kids are obsessed with these days, criminally underrated.