The third book in The Hunchback Assignments series is called Empire of Ruins. In it Modo, Octavia, Mr. Socrates and a few others are searching through the Australian rainforest for a lost temple that contains an ancient artifact called The God Face.
Here's the Canadian/Australian cover done by Christopher Steininger:
In theory the book will be out in January 2011 in Canada, February in Australia, and September in the US. I say in theory because I'm working on the revisions right now...
Must say I love this cover. Especially Modo's mask.