The Candy Shop War by Brandon Mull

In The Candy Shop War by Brandon Mull, friends Nate, Summer, Trevor and Pigeon think they've gotten lucky, making friends with Mrs. White, the owner of The Sweet Tooth, a new ice cream and candy shop that has been set up in town. At first, they think she's really nice. Especially when she gives them magical candy that give them magical powers as long as the candy is in their mouths. But as Mrs. White starts asking the kids to start stealing things for her, the kids realize they've gotten in over their heads.

But they can't get help from their parents, because the white fudge Mrs. White sells at her shop makes people not notice what would otherwise be obvious. Can the kids stop Mrs. White with the help of John Dart, a magical enforcer, and Mr. Stott, a good magician? Or will Mrs. White take over their town? Read the book and find out! The Candy Shop War was published in 2009.