Simplify the following text for a Grade 10 native English-speaking person.
Original: The book is internationally famous for its innovative style and infamous for its controversial subject : the protagonist and unreliable narrator , middle-aged Humbert Humbert , who becomes obsessed and sexually involved with a 12-year-old girl named Dolores Haze .
Simplified: It is a very controversial book , because of its unreliable narrator . The main character , Humbert Humbert , falls in love , and has sexual relations with a 12-year-old girl nicknamed Lolita .