Although the novel is often referred to as "a mystery", it is not an example of whodunit or detective fiction. Instead, the central puzzles are the origins of suffering and the motivations of unusual behavior. Characters appear in fragments, with brief scenes providing small clues about their identity. Vautrin, for example, slips in and out of the story – offering advice to Rastignac, ridiculing Goriot, bribing the housekeeper Christophe to let him in after hours – before he is revealed as a master criminal. This pattern of people moving in and out of view mirrors Balzac's use of characters throughout "La Comédie humaine".