Caterina is a teenager in a small rural city near Rome. When her unpleasant father gets a transfer to a school in Rome, everything is different. Girls make fun of her, girls help her, girls put something in her bag so she shoplifts, the cousin of a girl is not allowed to date her because his mother thinks Caterina is trash.
While they're exercising/running, the girl with the cousin provoked her by talking about her being trash. Caterina argues that she isn't trash, it's the girl's family that is, and the girl pushes Caterina into a pile of something heavy and when she gets up, the girl starts hitting everybody she can reach. She knows she won't get in trouble -- her father is the prime minister -- but Caterina runs away and a girl was hurt by the hitting. Caterina's father has become a little weird around teenage girls, and wrote a semi-porn novel that he insists is a bestseller and talks about what the movie will be like. He makes a fool of himself on TV talking about that, and is suspended from teaching.
Caterina makes her way home and is found by a boy from across the street, an Australian who, when he and his mother speak Australian, has the Italian translation on the screen. He takes her to his room where he can see into Caterina's apartment. He also tells her that he sees her father sit in the same chair all day, and her mother spending time with another man. When the father sees the mother with the other man putting up the laundry, he gets on his motorbike and leaves.
After a while, Caterina and her mother head for a beach vacation and the other man will join them on the weekend. They're happier than they've ever been and they hope the husband/father is happy, too.