When Clark was two years old, his parents divorced. His mother would later remarry around the time of his third birthday, to Gretchen's father. Though the two sometimes argue, they get along fine otherwise. One summer, while their parents are called away on a work emergency, Clark and Gretchen are forced to stay with their grandparents, who live in a mansion-like house, deep in the swamp. While Grandma Rose and Grandpa Eddie are kind, they are rather eccentric.
When they arrive at the house, the two can tell something's wrong. Grandma Rose and Grandpa Eddie seem overly paranoid. Even stranger, the two forbid Clark and Gretchen from entering a specific room in the house. When the two leave, the step-siblings are left alone. Curiosity getting the best of her, Gretchen enters the room and sets a swamp monster loose upon the house.
The monster proceeds to chase the children, forcing them to come up with ways to defeat it. Nothing seems to work until the monster attacks Gretchen. Realizing the two are humans, it reveals it is allergic and dies shortly after.
Leaving the house, the two find themselves alone in the swamp, hearing the growling of countless other monsters.
Clark loves comic books about monsters, but isn't at all brave when confronted with a real one. However, it is because of this that he loses his interest in horror. He seems to get along fine with Gretchen.
The book describes Clark as short, with curly brown hair eyes, brown eyes, and a face covered in freckles. Gretchen also reveals he wears glasses.
- Clark and Gretchen's surname is not revealed in the book or in the episode, but the tear-out trading card reveals it to be Allen.
- Although, it's unclear how both children would have the same surname if they're step-siblings. Unless they coincidentally had the same surnames all their lives, one of them would've needed their name changed.