Multiple chapters of Gary D. Schmidt's novel Trouble end with paragraphs written in italics. The speaker in those italicized portions is still the same third-person-limited narrator relaying the whole story; however, the narrator's focus switches in those sections from Henry to Chay Chouan.
Like all third-person narrators, a third-person-limited narrator is not a character of the story and instead relays the story as an observer, using third-person pronouns such as he and she. However, whereas a third-person omniscient narrator will get into the heads of every single character in the story, a third-person limited narrator will only focus on getting inside the head of one character. In Schmidt's story, the narrator focuses on getting inside Henry Smith's head. We can tell because Henry is the focus of every single scene; plus, the narrator relays only the thoughts and feelings of Henry through the narration. Numerous examples can be found throughout the book, but one example of the narrator relaying Henry's thoughts and feelings in the narrative text can be found at the end of Chapter 12, after Henry has had his first meal with his brother's killer:
He looked across at Chay. Who had murdered his brother, Franklin. And he felt anger rise in him and sour the chowder in his stomach. (p. 165)
In contrast, if we learn the thoughts and feelings of other characters, it is because they speak them aloud.
However, in the italicized parts, the narrator relays the thoughts and feelings of Chay, which we can also tell at the end of Chapter 12 when the speaker reflects, "But why would anyone eat a chowder?," immediately after Chay had refused to order clam chowder in the chowder house. Through these italicized parts, we learn multiple details about Chay's backstory such as what happened to his pet dog and why, that there was a girl with him in the truck when he accidentally hit Franklin, and that Chay was the one who set on fire the boarding house owned by Chay's own father.