Silvertree: A book about men and women who can travel between worlds

Simon Etheridge is one of a select band of men and women who can travel between worlds. There are many different versions of earth and many of them have humans on them. Every world is at a different stage of development but one thread runs true across nearly all the human worlds. Many of those worlds are ruled by a shape shifting reptilian race masquerading as humans and our world is no different. Simon has visited worlds where humans rule and our world is not one of them. Many people go to their jobs, bring their families up and live their lives with no idea that the ruling classes in many countries in the world are infested with shape shifting reptilians. Simon is determined to change that but the older people who can travel between worlds are cautious, not wanting to change the status quo. Because Simon is dangerous, Julia has been appointed as his guardian and mentor and she has guided him in the development of his powers. When on vacation on an island in Florida, Simon comes across a reptilian gateway to another world. He acts quickly before anyone can stop him, enters the gateway and kills the reptilian who controls it. Now there is a bounty on Simon's head and those who can travel between worlds have been told to give him up. Julia is determined to hide Simon on another world but first she must lure those out who would kill him. There is a bounty of much gold on his head so Simon will be sought by both humans and reptilians.