Balance Keepers, Book 3: The Traitor of Belltroll

The explosive conclusion to #1 New York Times bestselling author Lindsay Cummings's epic fantasy adventure series about a magical world at the center of the earth. The bestselling author of the Seven Wonders series, Peter Lerangis, says Balance Keepers is "filled with imagination and sneaky humor." In this third book, perfect for fans of Brandon Mull and Lisa McMann, the Balance Keepers must fight a dangerous traitor in an epic battle of magic.
Albert and his Balance Keepers teammates have been called back to the Core for immediate action! There's a serious Imbalance in the fantastical underground Realm of Belltroll. Without intervention, everything from New York to Yellowstone above could be swallowed by earthquakes. It's clear the mysterious traitor who caused last term's chaos is at it again, and with a vengeance. Albert's super-magical Master Tile helped fix the Ponderay and Calderon Realms in previous terms, but now it seems the Tile may be more trouble than it's worth.
Because if it's Albert's Tile the traitor is after, there will have to be a battle sooner or later, and only one of them can win.