Ollie is eager to help his Grandpa Gus plant a new section of his legendary prehistoric garden. However, Ollie’s "enthusiastic horns" lead to a soggy disaster when he accidentally breaks a water valve, flooding the entire yard and burying the new plants in mud. Through the squishy mishap, Grandpa Gus teaches Ollie a gentle lesson about resilience, explaining that like a garden, the most important part of ourselves is the roots that hold tight and help us grow back even after a mess.

After a massive thunderstorm leaves the playground at Cretaceous Creek Elementary covered in mud, Ollie and his friends discover a trail of enormous, mysterious footprints. Fearing a "super giant monster" might be lurking behind the supply shed, the Detective Club follows the clues—squashed leaves and bumped swings—to uncover the truth. They soon realize the "monster" is actually Mr. Bronto, the kind new school janitor, and the friends team up to help him build a brand-new playground for everyone to enjoy.