The Tennysons pick up the grandson of another Plumber named Cooper, who is hitching a ride home with them. Meanwhile, a Plumber base at Fort Knox is robbed by the Circus Freaks and Sublimino. By the time the Tennysons find out, they are too late to help. They soon learn of a second robbery, this one run by Rojo (having gained a new cybernetic suit), Animo, Clancy (mutated into an insect), and Charmcaster. Max discovers that they are searching for the keys to the "Sub Energy", an extremely potent sub-atomic power source given to the Plumbers by an alien race. They lose the keys to the villains, and attempt to rout them at the Mount Rushmore base, where the Sub Energy is stored. However, they find that the Forever King, joined by a subordinate and the villains that raided the earlier bases, has beaten them to it. He dubs his team the Negative 10 and sets them upon the Tennysons. Ben, Gwen, and Max, along with Cooper, use the Plumbers' Mount Rushmore installation to mount a final stand against the Forever King's forces. Max discovers that the Forever King was once a plumber named Driscoll who was kicked out after hoarding alien technology. Despite their best efforts, they are unable to keep Driscoll from obtaining the Sub Energy. Driscoll uses the energy to enhance his armor suit and battles Ben, who is able to use Upchuck to digest the power source and destroy it safely (he obliterates the remaining Mount Rushmore faces in doing so, however).
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