Shocked by the discoveries in the furthest reaches of the Dungeon, the City prepares to delve even deeper for answers. A surprise attack by the subterranean Undercity throws them into chaos, and a massive war soon rages throughout the Dungeon itself. The Undercity proves a wily foe, and against all odds the City finds itself struggling to gain the upper hand. And all the while, the Dungeon remains capricious, mysterious, and deadly.

Alex Kenderman is recruited by the supreme commander of the City, Mansa Musa Red, to lend his tactical expertise to the war effort. He and his party must fight against Underdwellers and the Dungeon itself to obtain victory, before it is too late. But two sinister questions remain:

Why did the Undercity start the war?

And who will win it?