Stanley and his monster find a book that shows them "How to Build a Tree Fort."

Hell is under new management, Heaven has taken over and the first order of business is to make sure all the demons are accounted for, but there is one missing. The Nameless one, is still on Earth and the angels in charge need to find him.

On Earth, the Nameless One, currently known as Stanley's Monster, is hanging with his best friend, Stanley and going through his parent's attic, looking for their next adventure. The pair of best friends find the 1912 classic book "Heterodyne Boy's Big Book of Fun" and quickly discover the chapter on how to build the greatest tree fort and agree that that will be their next adventure.

After learning from his father and mother that the Heterodyne Boys were real people and that their how to books, like the one he and his monster found in the attic, were real and having a dream about the Joker and the Justice League coming to join his tree fort, Stanley and his monster make a plan to build a tree fort in the neighbor's yard. The neighbor agrees when he sees that Stanley has the Big Book of Fun.

Stanley tricks a construction worker into giving him his extra lumber, and steals items from around the house in order to build and furnish the tree fort. That night Stanley and his monster sneak out and sleep in their new club house, but over night there is a large thunderstorm. Stanley's mom comes to check on him and he learns that is her Big Book of Fun. She then takes Stanley inside, never seeing the monster, who is now alone in the tree fort.

The monster is about to sneak back into the house but a crack of lightning startles him and he is suddenly face to face with Nyx.

Note: The Joker and the Justice League only appear in Stanley's dreams.