This incident happens when the neighbourhood children are all gathered in the street watching Miss Maudie's house go up in flames while the adults try (unsuccessfully) to put the fire out.
Apparently Arthur (Boo) Radley put the blanket around Scout, though she was unaware he was just behind her. As towards Jem when he patched up his pants, Boo shows his good will towards Scout when he sees her shivering in the cold.
This is the closest Scout gets to ever meeting her 'friend' until Halloween night when Boo fends off Mr Ewell from attacking the Finch children. In this way the children and the reader remain intrigued about Boo and a certain suspense is maintained until the very last chapter of the story. Then, true to his image, Boo just fades out of sight.
Boo Radley gives Scout the blanket as she watches fire burn down Miss Maudie's house across the street from hers. Scout is so absorbed in watching the fire and the action associated with it that she doesn't notice that Boo is also watching, and takes the time to get a blanket to put around Scout's shoulders.
In Chapter 8, Maycomb experiences an extremely cold winter and the Finch children spend their day off from school attempting to build a snowman. Later on that night, Atticus wakes his children up because Miss Maudie's house catches on fire. Atticus tells Jem and Scout to stand in the Radley yard at a safe distance while he helps the other community members retrieve Maudie's furniture from her burning home. While Scout and Jem are waiting in the cold, Boo Radley silently places a blanket over Scout's shoulders to keep her warm. Neither of the children are aware that Boo placed the blanket over Scout's shoulders. In the morning, the Finches are drinking hot chocolate and Atticus asks Scout who gave her the blanket that is on her shoulders. Scout and Jem are both confused, and Atticus tells them that Boo Radley must have given Scout the blanket. This news frightens Scout, and she mentions that she nearly threw up at the thought of Boo being so close to her.
While we are not directly told that Boo Radley is responsible for placing the blanket around Scout, we can infer that information from, among other things, Atticus's reply to Scout when she enters the house with the blanket itself.
As Scout is standing in the cool night air outside the scene of Miss Maudie Atkinson's burning house, she fails to notice the person who places the blanket around her. Given her location (just outside the Radley place), we are also led to conclude that Boo is responsible for the act of kindness. This gesture makes the second generous act that we may believe Boo is responsible for. Prior to this event, we are also led to believe that Boo (Arthur) is the party who places trinkets, candy, and treasures in the old tree's knot hole for the Finch kids.
well. ummm. once some one placed the blanket on Scout, she was sooo shocked over the fire. Later that night, Scouts father told scout that it was Boo Radley that placed that blancket on scouts shoulders