How does life change for the Dunbars after Penny's death in the novel, Bridge of Clay?

After the death of Penny, the Dunbars' lives are all changed. Michael Dunbar begins to leave home for days on end, until one day he disappears altogether. This earns him the nickname of "The Murderer," as the boys feel he has all-but killed them. Matthew, the oldest boy, becomes the breadwinner and parent-figure for his brothers. Clay becomes quiet and insular, and takes to punishing himself by running long distances and fighting with other boys. Rory is expelled, whilst Tommy collects a strange variety of animals, including a mule, which he names after characters from his mother's favorite books. In this period, Clay falls for a new neighbor, Carey Novac, who is a trainee horse racer. They become close, and Clay shares his secrets with her.