On Halloween night, Dermott and Hank dare Dean to go into a nearby haunted house. Meanwhile, Orpheus, Alchemist and Jefferson host the Brimstone Assembly while Rusty and Hatred take bets on whether tricker-or-treaters will make it through the defense system.
In the aftermath of the Venture Halloween party, Rusty works desperately to complete a subcontract job for J.J. However, he recruits a team of interns which soon start displaying odd mutations. Meanwhile, Dean makes some startling life changes after Triana dumps him, and Twenty-One tries to convince the Monarch that he's no longer working for him.
General Manhowers sends the Ventures to Central America to recover a Venturestein that is manufacturing. However, Dean refuses to go, Hank gets high on caffeine beans and becomes a jungle vigilante, and Rusty discovers that Venturestein wants to form an Abomi-Nation of creatures like itself.
Twenty-One recruits some new henchmen to join his SPHINX organization, unaware that their members of the old villainous SPHINX. Meanwhile, the Monarch and Dr. Girlfriend infiltrate the Venture compound posing as beaver inspectors in a bid to plant explosives and destroy Rusty once and for all.