In a world where everyone is a cereal mascot and cereal is grown on farms, Penn seeks the help of an imprisoned Rippen to catch the Milkman, a villain threatening to flood all the cereal crops with milk, turning them soggy.
- The title refers to the time-honored pun of "cereal" ("derived from or relating to grain") and "serial" ("referring to a number of actions or events that happen in a particular time-sequence"); a "serial criminal" is one who commits a number of similar unlawful actions over a certain period of time.
- Paul Reubens (Pee-wee's Playhouse and Tron: Uprising) guest stars as The Milkman.
- This is the first episode in which Rippen isn't the main villain, as the Milkman is instead.
- The brief appearance of "Lenny the Lion" is likely a reference to Linus the Lion-Hearted, a 1959 cartoon created to advertise various Post cereals such as Alpha-Bits, Crispy Critters, Post Toasties, Rice Crinkles, and Sugar Crisp; Linus himself was voiced by well-known character actor, Sheldon Leonard. (Get it?) In addition, the Alpha-Bits mascot, a friendly, Southern-accented Postman, Lovable Truly, is very similar in depiction to The Milk Man in this episode.
- This episode reveals Rippen and Larry's jobs as an art teacher and school principal respectively.
- "We Can Catch the Milkman"