how does max ecsape from stuttgard after the war breaks out?

Walter gets ahold of Hans who had promised Max's mother anything when his life was saved by her husband in WW1. Hans agrees to hide Max in his basement and sends the key to his house inside the front cover of Mein Kampf, a book written by Hitler. In an ironic twist, it is this book that holds the key to Max's life. Max stays in the Hubermann's basement which is where he meets Liesel.