The Picture of Dorian Gray by Oscar Wilde
Lord Henry is rich, idle and curious and amuses himself by trying to corrupt the beautiful boy, Dorian. He is successful beyond his dreams because Dorian embraces his lifestyle--far more seriously than does Lord Henry himself so that in the end when Dorian asks him what he'd say if he told him he'd killed Basil (whose mysterious disappearance has been the talk of London society), Lord Henry replies that he wouldn't believe it, because only the lower classes actually commit crimes.
In fact Dorian did kill Basil after showing him the portrait which after many years shows not only age but the dissipation and cruelty into which Dorian has fallen. Basil's horror causes Dorian to kill him and then to bribe an acquaintance to get rid of the body. What the bribe was we never know but the man killed himself rather than live with what he had done. As had an innocent girl many years before whom Dorian wooed and then cruelly left. We're to assume there were many more such betrayals in between.
Early in their relationship Lord Henry had given Dorian an 'immoral book' the contents of which we can only imagine. Dorian seems to have taken it as a guidebook. One imagines that Lord Henry found it primarily amusing and was amusing himself to see its affect on Dorian. And Wilde, of course, is playing with the idea of whether or not a book can be immoral as critics of the time pondered the idea of whether a book written by an immoral man could be a good book.
Today when Wilde is taken seriously as an artist and his homosexuality seems quite irrelevant, these issues of morality in art or in human conduct are still as perplexing as they were when the novel was written.
The dialog in this novel, quite apart from the heavy Gothic plot, is quite as delightful as The Importance of Being Ernest or Lady Windermere's Fan.