When lightning hits Little Oak, one of Will and Mina's villager friends gets struck-and turned into a witch! Mina and Will sprint straight to the witch huts in the swamp, trying to save their friend. But instead of help, they find grave danger: witches with potions so powerful, Mina's own potions seem weak and useless.

When Mina falls victim to a witch's potion, it's Will who has to perfect his potion-making skills. Can he remember what Mina taught him in time to save her from the deadly secrets swirling deep within the swamp?