Very few novels have unsettled me as this one. It begins as a study of addiction, sex addiction in this case, with all the evasions, denials and behaviours of the addict depicted thoughtfully and with feeling.
The protagonist, Harry, has moments where he is aware that something is very wrong. Intermittently he senses how fulfilled he could be, and how the good things of his life really could be his salvation (a loving family, a passionate, loving marriage, children). But such moments of bewilderment change to horror as the stakes are raised.
His 'demon,' his addiction or obsession, leads him into more and more dangerous situations as it escalates the game, intensifying the need in Harry so that his drug of choice moves from casual sex, to dangerous sex, to petty crime, and then to the shocking acts of the novels conclusion.
The writer, unfortunately for your sleep, makes you care deeply for the protagonist, as his capacity for destruction increases with his outward success. The action takes place in Harry's tortured thoughts, and through the viewpoints of those close to him. The writing is brutal and poetic, stripped down and lethally accurate in its meaning. Not one word is superfluous in this brutal prose poem.
Incredible, exhilerating, but profoundly disturbing. Be prepared to be introduced to some of your own demons.