Dean W. Arnold is an author and filmmaker here in Chattanooga whose style is described as “History with a plot.” His just-released book is called “Unknown Empire: The True Story of Mysterious Ethiopia and the Future Ark of Civilization.” On Monday evening, starting at 6 PM, he will be at The Mad Priest Coffeehouse here in Chattanooga for “An Evening in Ethiopia” - celebrating his book , and featuring a traditional Ethiopian dinner and coffee ceremony. And on Tuesday evening, starting at 5:30 PM,