A 13-year-old boy named Jack Sullivan imagines himself as a pirate captain as he and his crew ride over a mall, carried by a giant monster named Mallusk. Mallusk stops short as a massive skeleton army, led by a monster named Thrull, heads toward the Tower.

Thrull plans to build the Tower to bring Ŗeżżőcħ, an evil, world-destroying entity, into this dimension. In the previous book, Thrull needed a crucial piece of building information hidden in the brain of a monster named Ghazt. He took Ghazt to see the “mad doctor” Wracksaw, who retrieved the information. Jack and his crew tried to thwart Thrull but failed, and Thrull got the Tower plans. When Ghazt died, the energy release shot the whole fortress into the monster dimension along with their new Goon Platoon friends. Now, Jack and his friends speed toward the Tower, hoping to find a way to stop Thrull.

Jack wonders how they’ll take on the skeleton army. In the moment before Ghazt blew up, he transferred some of his zombie-controlling powers into Jack’s Cosmic Hand, an alien tentacle that has merged with Jack’s hand, giving him mysterious powers.