Cat Mummies by Kelly Trumble
I checked this out to preview for the middle school years. My boys saw the book and begged me to read it to them. I thought they'd get bored quickly but they LOVED it. We read the whole thing. The book moves fairly quickly and is easy to follow. They acted out several of the battle scenes described.
A caution: it does deal with animal worship and spirits so we talked about that in reference to our beliefs. Other than that it is best used as a middle school read-aloud or a junior high independent BUT my then first graders enjoyed it an understood it so I wouldn't hesitate to read it to all my kids.