The Princess in Black and the Science Fair Scare by Shannon Hale

Princess Magnolia is excited to go to the Science Fair to present her poster about seeds and plants. But when she and her friends arrive they find a surprise goo monster at the fair. This is a job for the Princess in Black and the Princess in Blankets! But will two masked heroes be enough to save the science fair? A little scientific problem-solving – and a lot of princess power – will make the sixth entry in the New York Times best-selling series a smash hit.