Pendragon book #3: The Never War

The main character of the book is Bobby Pendragon. Bobby is a traveler, he uses things called a flume to travel to the other "worlds" as i call them. For this trip Bobby goes to first earth, where he gets trapped by gangsters. First Earth is the earth but in the past to be exact the date is May 11, 1937. Bobby meets Saint Daine (he is the bad guy) in the city but Saint Daine can change is body to look like anyone, so Bobby doesn't know its him.