H. G. Wells' 1897 thriller The Invisible Man (available here) still holds up after all these years! The plot -an albino scientist named Griffin in late 19th century England manages to create an irreversible process that turns him invisible, and eventually insane- is pretty familar to most readers. But what kept me focused was the depiction Wells gives of Griffin.
At first, the reader feels sympathy for the character, as Griffin seems to just want to be alone with his experiments in restoring his visibility. The reader will also take Griffin's side when he reveals himself to the nosey residents of the boarding house he's taken refuge in at the start of the book. The story seems to be becoming a light, humorous lark.
But things take a dark turn when Wells starts revealing Griffin's true motivations. A man who stole money from his father (subsequently driven to suicide) to fund his experiments, Griffin naturally finds it easy to rob others using his invisiblity. Though he's obviously losing it, sanitywise, Griffin very easily rationalizes that he can get away with staging a "reign of terror" throughout the country, and proceeds to commit various crimes. But the best laid plans don't always come off...
Despite his amorality, Griffin makes an interesting figure. The reader hears the character's explanations for his actions and sees events as Griffin sees them. Griffin's interactions with the other characters in the book, such as Thomas Marvel, the tramp who briefly becomes the Invisible Man's confederate, former associate Dr. Kemp (to whom Griffin spills the beans about his "discovery"), and the innkeepers Mr. and Mrs. Hall, also bring out various shades of his psyche.
Written early in Wells' career, The Invisible Man moves along in a brisk but exciting and economical style. There are several nice touches throughout the book, my favorite being what becomes of the food Griffin digests (it's not pretty). The climax is a haunting one that'll stay with you long after reading. Check it out!
(And though it takes liberties with some of the characters, director James Whale's 1933 film version, available here in VHS, is also strongly recommended.)