Meet The Kreeps The Mad Scientist : No. 4 by Kiki Thorpe

Polly's mad-scientist stepbrother, Damon, spends hours in his creepy basement lab, preparing to enter the school science fair. Polly doesn't know what's worse - that Damon is clearly up to no good, or that he might actually win first place at the fair! Can she stop him before he unleashes his 'experiment' on their school?