Full Moon Fever

Full Moon Fever is the twenty-second book in the Goosebumps Series 2000 book series. It was published in 1999.

The cover illustration depicts an unspecified beast in a forest wearing ripped pants with the full moon in the background.

Plot
Robbie and his sister Alesha are visiting their Grandpa John at his cabin in the woods, which they don't want to go because they hate his scary stories that keep them up at night. He tells a story about Full Moon Fever, a mythical illness which turns anyone who looks at the full moon into ravenous, snarling beasts. He heard about it from a woman he met after getting lost in the Canadian wilderness. After he pretends to have caught it as a joke, they brush the whole thing off and try to forget about the story.

On Halloween night, Robbie and Alesha go trick-or-treating around town. They reluctantly visit the home of one of their nastiest teachers, Mrs. Eakins, who they'd recently upset by kicking a soccer ball through her window. When they arrive at her home, however, they are surprised to find that the usually mean Mrs. Eakins is being so friendly. Mrs. Eakins generously gives them both full-size candy bars which the two gobble up on the way back. Robbie suggests that they should prove if Grandpa John's story is true, by looking at the full moon. So, they do exactly that, but start to feel sick.

The next morning, Robbie discovers that he is completely coated in thick hair. He goes to see if Alesha has turned into a beast like he has, and unfortunately, she has. They call for their mom, but she doesn't recognize them. They escape the house when their mom begins to call the police. They find they have an immeasurable hunger. After regaining their speech, Robbie and Alesha plan what to do. They worry that they have succumbed to Full Moon Fever. Robbie and Alesha go to find their Grandpa John, who told them about the disease the night before, only to discover that it is merely an old legend and that it isn't real.

The two travel to Canada to find a cure and meet up with the woman who told John the story, but she tells them she made it up and has no idea what to do. However, there is a man named Dr. Thorne that she thinks may know something. They go to him and seemingly meet his son, only for it to be revealed that this is Dr. Thorne, who pretends to be his son as he doesn't have one. He then turns out to be evil as he captures the kids and turns them into circus freaks. After spending a few weeks in captivity, they eventually escape the circus and try to change back under a full moon, only to find it has no effect.

They return home with Grandpa John and find Robbie's Halloween candy, including a "Best" bar that actually says "Beast Bar", leading Robbie and Alesha to discover that the candy bars Mrs. Eakins gave them were actually cursed and she is a witch. Robbie and Alesha go to Mrs. Eakins' home and attack her after ransacking the house. They eat many "Cure Bars", which were lying around the house and hope that they will cure them. Mrs. Eakins then curses them to shrink and they start to shrink. Robbie takes another look at the label and discovers that it actually says "Curse Bar", meaning that they have just likely permanently cursed themselves.

International releases
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Differences

 * In France, this book is the 68th of the original series.
 * Robbie is called "Bobbie."
 * In the UK, the book's page count is changed to 123.
 * Additionally, the excerpt on the back cover was also changed in the UK. The last line changed to  'Stared wide-eyed at a monster...' .

Trivia

 * This book's title is a reference to the Tom Petty album Full Moon Fever.
 * This book's plot resembles an earlier short story, "Pumpkin Juice", from Still More Tales to Give You Goosebumps.
 * The concept of the protagonists being cursed by a woman in town who turns out to be a witch is similar to Chicken Chicken.
 * The concept of a vindicate elderly woman initially appearing to be nice is similar to the short story Marshmallow Surprise.
 * This book references Zorro, Teletubbies, Hershey Bars, and Milky Ways.
 * Throughout the entire book, Robbie's gender is never explicitly revealed.
 * "Robbie" used to predominantly be a girl's name, but it slowly became more popular as a boy's name over time. "Robbie" could also be a nickname for Robert, Roberta, Robin, Robyn, etc.
 * Presumably, Robbie is a boy. If Robbie and Alesha were brother and sister, it would align with Stine's penchant for including one male and one female protagonist. Plus, Robbie chooses to dress up as a male character for Halloween. However, there's technically nothing stopping readers from assuming Robbie is a girl. Interestingly, a review in The Hamilton Spectator refers to Robbie as female.
 * The preview given at the back of The Haunted Car contains a slight difference ⁠— besides chapter 10 ending early. The line "Come on. Let's see if the story is true." is presented as "Come on. Let's see if the story Grandpa John told us is true." This difference may have been included to give extra context to the preview.
 * After Robbie and Alesha looked at the moon, they felt sick. But later it was revealed that they transformed because of the Beast Bars. It is unknown why they felt sick, since Full Moon Fever doesn't exist (in this book).

References in other Goosebumps media

 * There is an event based on this book in Goosebumps HorrorTown