Gretchen Allen

Gretchen Allen is the main protagonist of the forty-sixth Goosebumps book, How to Kill a Monster, and its accompanying television adaptation. She is the stepsister of Clark Allen

History
Gretchen's mother and father divorced when she was very young. Around her third birthday, Gretchen's father married a new woman. The woman had a son named Clark, and he was roughly same age as Gretchen.

One summer, Gretchen and her stepbrother are taken to stay with her grandparents, Grandma Rose and Grandpa Eddie. The couple lives in a mansion-like house in the swamp.

As time goes on, the step-siblings begin to notice that Grandma Rose and Grandpa Eddie are acting strangely. The couple tries to forbid the kids from entering one particular room, but the kids end up going inside while the adults are away. By entering the room, Gretchen accidentally release a swamp monster that had been trapped inside. The kids find two letters from Grandma Rose and Grandpa Eddie. The first note explains that the monster sneaked into the house, but the couple had to way to remove it. Their only option was to trap the creature in a spare room.

The kids try to kill the monster with various methods, but they can't seem to do it. The monster attacks Gretchen, but it falls dead, revealing that it's allergic to humans. The kids run outside, into the swamp, and open the second letter. The letter tells the kids that, if they kill the monster and leave the house, they should avoid the swamp at all cost and stick to the road. The letter suggests that there could be dozens of monsters in the swamp. The kids then hear monsters growling all around them in the swamp.

Personality
Gretchen is fairly agreeable, as she gets along well with her stepbrother and stepmother.

Physical appearance
Gretchen's hair is long, straight, and blonde. She has green eyes and says that she looks quite a bit like her father.

Trivia

 * 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.