Grymbeard is a dwarven inventor who has spent his life in the shadow of his royal brother Wilbur, and he is done with it. His plan for revenge is methodical and enormous: a giant mechanical war-automaton fueled by mysterious Darksteel, assembled in secret deep in the Darksteel Mountains. As the machine nears completion and its capacity for destruction becomes clear, the Alliance — a coalition of Linirean sharpshooters, Dark Army mages, and other defenders — mobilizes a five-stage campaign to infiltrate the mountain, work through Grymbeard's army of mechanical clones and escalating bosses, and dismantle the automaton before it wakes.