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 they're 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.
Dr. Venture takes the team along for his annual visit to the Greek island of Spanakos for the Spanakopita festival. However, Sgt. Hatred soon suspects that there's a dark secret behind the island festival. Meanwhile, St. Cloud travels to the island to defeat Billy once and for all.
When Monstroso and Molotov are captured by the OSI, a bizarre series of events occur and IA conducts an investigation into what really happened.
Hank and Dermott's prank on Rusty goes horribly wrong, and Hank gets himself committed with Twenty-One to fix things. Meanwhile, Dean goes to visit the secret woman in his life, and Dr. Orpheus makes a dramatic entrance.
When the OSI identifies one of the Council of 13 members, they send a civilian undercover to get close to him. However, the mission goes horribly wrong when their volunteer ends up at a villain club along with the Council of 13 and... Rusty Venture.
Guest Stars: James Urbaniak
as Phantom Limb | Christopher McCulloch
as Sgt. Hatred / Hunter Gathers / Ghost Robot / Dragoon / Dr. Z / Don Hell / Steppenwolf / The Nerve / Sovereign Head / Dr. Henry Killinger / St. Cloud | Kevin Conroy
as Captain Sunshine | Doc Hammer
as Shoreleave / Billy Quizboy / Paul Monocle / Vendata / Sunsational | Paget Brewster
as Amber Gold / Vespertina / Councilman 11 / Waitress | Bill Hader
as Phineas Phage / Headshot / Flying Squid | John Hodgman
as Snoopy | Larry Murphy
as Monsenor / Bouncer / Wonderboy 5
When Rusty is apparently killed by the Monarch, Hatred sends the boys off to live with their godparents, and then turns to Twenty-One for help to infiltrate the Flying Cocoon and recover Rusty's body.
Guest Stars: Christopher McCulloch
as Sgt. Hatred / Action Man / Col. Gentleman / Pete White / Tim-Tom / Brainulo / Humungoloid / Henchman 86 / Kiki / Thug | Doc Hammer
as 21 / Billy Quizboy / Rose / Kevin | Bill Hader
as Flying Squid