In a
cold opening with the
theme music,
Phineas and
Ferb warn the audience that the program will be frightening, disturbing, and horrifying. Ferb chokes up a hairball, and Phineas says "You've been warned." When the episode officially starts, Phineas is feeling disappointed by the pouring rain and
power outage, canceling his plan to stand in the middle of a field with a metal rod, until his step-grandfather Reginald starts to tell the stepbrothers the story of their ancestor, Ferbgor, a
hunchback henchman of the
Victorian era who assists his master Dr. Phineastein, a mad scientist, in gathering
platypus body parts to create a platypus monster and enter him in a "monster ball". Meanwhile, Perry heads over to Doofenshmirtz Evil Inc. to find out what Doofenshmirtz's current plans are, but he accidentally locks himself and Doofenshmirtz in his apartment (due to the storm that is causing Doofenshmirtz's security system to go haywire), much to Doofenshmirtz's anger. Realizing his mistake, Perry has no choice but to make himself comfy in Doofenshmirtz's place until the power is back on. As the two nemeses sit while drinking some hot cocoa, Doofenshmirtz tells Perry the story of his Victorian ancestor,
Dr. Jekyll Doofenshmirtz, who attempted to impress an
angry mob by transforming himself into a beast using a formula-making machine: the Concoction-inator, only to fail and become a
fairy princess instead. In Reginald's tale, Phineastein and Ferbgor construct and bring their monster to life, which frightens, then angers their castle
governess, Constance, and provokes her to rally the mob against them (referencing Candace's attempts to bust her brothers). The two are unaffected by her intentions and train their beast, rather poorly, so he will be ready to participate at the monster ball. In the meantime, Jekyll rectifies the problem with his formula-making machine and transforms himself into a hulking monster. He then goes to the village to torment the citizens and cause mayhem (though it seems that he's only doing childish pranks rather that just going out on a real rampage). During his rampage, he upsets the platypus monster and is chased all over the village by him. Phineastein and Ferbgor go looking for their creation and find him thanks to an unnamed Isabella Lookalike. The platypus monster has ended up at the monsters' ball. Before Dr. Phineastein and Ferbgor enter the ball, the monster viciously batters Jekyll and eats him. In the present, the power returns and Doofenshmirtz rushes Perry off to the door, telling him to come back tomorrow for his next evil scheme (however, he was going to have a scheme, but didn't have time due to the chiropractor). Doofenshmirtz then wonders what was the conclusion to the story. In Reginald's story, Phineastein and Ferbgor find the monster and the winner of the ball is announced: it is Constance, who has accidentally drunk Jekyll's formula and transformed into a beast, herself, and gets chased by the mob, presumed to be captured or killed. With the story concluded, Reginald reveals that he has completely forgotten everything he has just related because of his
senility. Ferb closes the episode saying that "platypus monsters are the only monsters to lay eggs." ==Voice cast==