The Bad Girl is a novella written by R. L. Stine. It was first published in 1999 and was the fourth book in the New Fear Street book series.
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Dawn and Jan never liked science class. But when they stumble across a formula that brings the dead back to life, it becomes their favorite subject. Jan came up with the formula. She was just fooling around--she didn't expect anything to happen. But now the formula is bringing things back to life. A frog. A dog. A human being. And they're coming back evil.