Heidi's parents died, and I actually feel sorry for her because she's pretty down at the start of the book. She had to move across the country to live with her Uncle Jekyll, and all she really remembers about him is that she once asked if he was Frankenstein because he has a fully stocked lab and works as a scientist.
After she gets off the train, she notices that her uncle isn't there to pick her up. She does meet a young man from town named Aaron. He tells her about a creature that keeps attacking the village, and he makes it clear that no one likes her family. When she asks for help getting there, he gives her some directions. He also makes it clear that he has no interest in walking her home or going anywhere near the house.
Heidi sets off and finds the house pretty fast. Her cousin Marianna rushes out and warns her to leave and get out. Before she can elaborate, the housekeeper comes out, welcomes her, and shows her to her room. Marianna keeps telling her to leave her uncle alone because he's a busy man and always working, but Heidi goes down to his lab anyway. He seems excited to see her, but like Marianna said, he's super busy.
Dinner time is always odd at the house. Marianna and her dad barely talk, and when they do, it almost seems like they talk in code. One night, Heidi hears screams coming from the village. When she looks outside, she runs into her uncle who says that he didn't hear anything. She goes into town the next day and finds the village ripped apart. She screams that it wasn't her uncle, and a reporter demands that she take them into the house. A group of locals grab her and throw her around, saying that her family is filled with creatures. Aaron manages to save her, telling the crowd that she's new and doesn't know anything.
At dinner, her uncle asks Marianna if she plans to go into town and she just shrugs. Heidi finds it odd because she hasn't yet seen her cousin leave the house. While wandering around later that night, she accidentally finds an old journal hidden in a secret area of the bookcase. It's filled with notes from someone who keeps changing into a creature. She thinks that it might be the journal of the original Hyde and gets pretty excited.
Heidi eventually starts questioning her uncle and wondering is he is the creature. She sneaks into his lab and sees him drink a bunch of potions and start changing before running out of the lab. He also locks her in her room one night, and she later catches him listening to her on the phone.
This all leads up to the creature attacking the town again. Heidi goes outside, and the creature turns and attacks her. Jekyll comes running up to help her. He grabs the creature and it slowly transforms into Marianna. He explains that she got bit by a weird fairy creature on vacation and she's changed every night since then. He keeps working on different potions to save her.
The villagers all attack and set fire to the house, but they make it into the lab. Jekyll has an escape route that will lead them away from the house and to safety. Heidi tells them to go along while she runs upstairs and finds the journal. She manages to grab it just in time for the villagers to grab her and drag her outside. Aaron saves the day again, and he manages to pull her away from the crowd.
Heidi goes to stay with Aaron's family until they can find some more of her family. She decides to tell him about the journal, and while flipping through it, he finds a page that says it's Marianna's journal. It turns out that she just used an old journal to record her feelings about becoming a creature. When Heidi gets to the last page, she swallows hard and blinks it shock. The last page reveals that Marianna watched her sleep one night and bit her on the shoulder.
*Yeah so that Marianna twist was not a real twist. Marianna is constantly sneaking around and dropping cryptic comments that show she's the creature early on.
*Aaron is such a random character. It's not like they hang out or anything. She meets him at the station, and then she doesn't see him again until he needs to save her. God forbid a girl be able to save herself.
*The first few pages actually are pretty sad! Heidi starts talking about how she cries every time she thinks about her parents, how she has really dark periods because of their deaths, etc.
*This book is so outdated even for the late 90s. The townspeople hated Jekyll as soon as he moved there because they knew he was trouble just based on his name.
*The image of people driving cars up the hill to torch an old house made me giggle.