While trick-or-treating with Candace, Phineas and Ferb meet up with their friends. Phineas is dressed as a vampire, Ferb is Frankenstein's monster, Candace is Heidi, Perry is Igor, Baljeet is a daisy, Buford is a pirate, and Isabella is a fairy princess. While walking, they come across a house that they have never seen before. As they approach it, they meet a boy hiding in a bush named Russell. Russell says that hiding in the leaves makes him feel warm and secure, relatively speaking. Baljeet asks why he does not go inside his house and Russell confirms that it's haunted. Phineas decides that they should help Russell by busting the ghosts, and Russell reluctantly follows.
Perry enters his Halloween-decorated lair through a jack-o-lantern, where Carl greets him, dressed as Major Monogram. Major Monogram, dressed as Carl, gives him his mission by telling him of some strange sightings: the Danville golf course has been chewed down to bare dirt, strange howls at the moon have been heard, cow-related graffiti at every leather shop in the Tri-State Area, and a crop circle shaped like a cow.
Phineas, Ferb and the gang enter the house with Russell, and to Phineas's surprise, his EMF meter picks up a 78. Suddenly, the jack-o-lantern in front of him grows into a scary humanoid with a pumpkin head, and asks the children if they aren't a little young to be hunting ghosts. They reply with a terrified "Yes, yes we are!" before running off, the monster at their heels.
Perry enters Doofenshmirtz's apartment to find that he has chained himself up. Doofenshmirtz explains that a few days ago, he declared war on grass, so he got himself a cow, the natural predator of grass. However, the cow was too slow, so Doofenshmirtz invented the Mind-Transfer-Inator to motivate the cow to work faster. Instead, Doofenshmirtz developed gaps in his memory, a strange craving to lick salt, found himself watching the nightly farm report as well as the pasture channel way more than usual, and because of this, he suspects that he is no longer human, which is why he needs to tie himself up. All of a sudden, he begins to transform into a were-cow, and breaks the restrains. The Doofenshmirtz were-cow runs off into the streets with Perry pursuing it with a lasso.
Back in the haunted house, Candace desperately tries to open the locked door. Russell comments that sometimes the floor gives out, which is exactly what happens. The children fall into the ghost-infested graveyard basement, where the monster continues to chase them into a red lake, and Baljeet comments that the liquid is the wrong color and viscosity for water. Zombies rise from the "water", and the terrified children continue to run.
After watching a news report on the were-cow, the locals form an angry mob, while Perry finds Doofenshmirtz in his human form in the middle of a crop circle. Doofenshmirtz tries to go with Perry, but is transformed again as the clouds part from the full moon. The angry mob finds them, and they pursue the were-cow into the streets, trampling Perry in the process. The mob becomes covered in flour after chasing the were-cow through a cooking class.
The jack-o-lantern monster has the children cornered in the basement. Ferb throws a skull at it, knocking its head off. As sparks fly from its neck, the children realize that it was a robot. They then learn that it was Russell, along with his parents Waylen and Mona, who had been tricking them with their animatronic haunted house. The EMF meters had been picking up on hidden frequency emitters. Impressed, Phineas asks for one more trick. Just then, the were-cow busts through the wall with the angry mob close behind it, trampling Candace. The children applaud, mistaking the flour-covered mob for ghosts, much to the confusion of Russell and his parents.
As the children go their separate ways for the night, Phineas is surprised to see that the haunted house is gone, only to see Waylen deflating it for the season. Phineas says that this is about the time in cliche Halloween stories when someone really turns into a ghost. Phineas and Ferb stop and stare suspiciously at Russell and his parents for a few seconds, until Russell tells them that it's not going to happen. Phineas then says goodbye and that they will see them next year.
- "Were-Cow on the Rampage"
- "Were-Cow on the Run"
|Vincent Martella||Phineas Flynn|
|Ashley Tisdale||Candace Flynn|
|Thomas Sangster||Ferb Fletcher|
|Dan Povenmire||Dr. Doofenshmirtz|
|Jeff "Swampy" Marsh||Major Monogram|
|Dee Bradley Baker||Perry the Platypus|
|Alyson Stoner||Isabella Garcia-Shapiro|
|Maulik Pancholy||Baljeet Tjinder|
|Tyler Alexander Mann||Carl|
|Bobby Gaylor||Buford Van Stomm|
|April Winchell|| Mona|