In this chapter, Miss Maudie's house catches on fire, and burns to the ground through the night. Atticus lets Scout and Jem come outside and watch as neighbors and other townspeople try to put out the flames. Unfortunately, they are not successful, and Maudie loses her house. The night wears on, and Scout, who gets colder and colder, doesn't realize that someone placed a blanket on her shoulders at some point in the night. In fact, she doesn't notice it at all until Atticus, returning from his efforts at the fire, points it out. At first, he thought that they had gone into the house and grabbed it, but when Scout confesses that she didn't know how it got there, he concluded,
"We'd better keep this and the blanket to ourselves. Someday, maybe, Scout can thank him for covering her up...Boo Radly. You were so busy looking at the fire you didn't know it when he put the blanket around you."
Boo had managed to come outside and cover her without her ever even realizing it. This quote can be found at the very end of chapter 8; I'm not sure what page number, because every version of the book is different, and I don't know what version you have. But look a copule pages before the end of chapter eight. I hope that helped; good luck!