What violent events occur on Mary Alice and Joey's first night at Grandma Dowdel's house in the novel, A Long Way from Chicago?

On their first night at Grandma's house, Joey is startled from his jigsaw puzzle by the sound of a loud blast outside the front door. Grandma and the children look out to see that someone has blown up Grandma's mailbox. Meanwhile, Effie Wilcox's home is also attacked and thugs have destroyed her outhouse.