As a special treat for her class, the school arranged for the kids to take a tour of Zuckerman's Zonked, which is candy factory in town. Mr. Zuckerman, who inherited the factory from his dad, gives them a tour and lets them sample some new candies. He makes a big deal out of his new candy, which will last as long as an all day sucker, be as sweet as chocolate, and as chewy as caramel. After showing them the recipe, he puts it in his pocket and gives them a tour of the library. It's only after going through some recipe books that he realizes his own recipe is missing.
Nancy names her first and primary suspect as Josie, a girl in her class who wants to run her own candy company one day. Mr. Zuckerman tells them that the secret ingredient is maple syrup, which is why Nancy gets suspicious walking by Josie's house that night and smelling maple syrup. Josie shows up to school the next day with a new candy that tastes gross. She wanted to recreate the recipe for him.
Her next suspect is Stevie, a boy who took the tour. She sees him acting weird and then hiding in a classroom. When she goes in, he explodes at her and spills a big bag of sugar. Mrs. Reynolds, one of their teachers, makes Nancy leave and tells her not to mess up his secret. She suspects they're working together until she finds out he's been working on a sweet recipe to lure insects away from his mom's garden.
The whole gang heads to Double Dip for some ice cream and finds a big sign out front that advertises its new line of candies. Andrew, one of the guys from their class, buys a triple ice cream cone and leaves without paying. They suspect that Andrew stole the recipe and gave it to Cathy, the owner, in exchange for free treats. Carson encourages Nancy to just ask people to find out the truth.
She goes back to the ice cream shop and sees Andrew again. It turns out that he got a gift certificate for his birthday, which was why he bought something without paying. Nancy then tells them what she thought, and Nancy tells her that the River Heights Dairy makes candy for their ice cream. The dairy made too much in this batch and gave it to her to sell. She tells Nancy that asking for the truth is a smart and responsible thing to do, and she's so happy with the girls that she gives them free candy.
They head to Bess's house and find her mom making maple syrup candy. Nancy suspects Bess until Mrs. Marvin tells them that she got a can of real maple syrup from a friend in Canada. The girls then decide to go back to the factory and apologize to Mr. Zuckerman for not solving the mystery. He tells them that it's okay, but Nancy then sees a sucker stuck to him and asks to use the library.
There, she digs through the books he showed her class and finds the recipe stuck to the back of one. Working in the factory leaves him covered in sticky stuff all the time. He thought he put the recipe in his pocket, but it was stuck to his hand and rubbed off on the book. He's so excited that he gives them all free candy to take home and decides to name a new candy after Nancy.
*Josie brings a Fluffernutter sandwich, chocolate milk, a bag of sugary cereal, and candy with her to lunch. That's a lot of sugar for one little girl!
*The candy factory looks just like stacks of jelly beans, and I have no idea how the builders did it. There's also an open mouth that you walk through to get inside. Why can't places like this exist in the real world?
*Zuckerman makes a Candy Baby, which is a cherry flavored sucker shaped like a baby that sounds like nothing I would want to eat. He also makes a new candy that uses little pieces of chocolate shaped like toast with peanut butter and marshmallow cream inside. I need to get me some of those.
*While walking with him back to the library, Nancy looks over and realizes that Bess is eating a chocolate bar that she somehow picked up along the way. When he asks how he can thank them for finding the recipe, Bess immediately says candy while Nancy gives her that look. I'm with Bess on this one.