Milford Spitz and the Very Fast Machine — James S. Hoch

Two pre-teen runaways team up with the school bully, only to learn that he has the coolest way for them to get away -- a very fast machine that travels in space, dimensions and time. Their adventures soon become entangled with a diabolical dictator who is obsessed with the power of time travel. Now giants, mysterious shadow creatures, and Professor Albert Einstein are all part of Milford's new middle school education.