In Ditch-a-Roo, someone is ringing Katharine’s doorbell and then disappearing. Her cousin Crockett tries to convince her it’s the Invisible Man but by using her detective skills she eliminates all the suspects except one: Vanessa. Katharine doesn’t unravel the mystery until she accidentally spills water on Vanessa’s science project. The “spark in the dark” experiment complements the information about electricity discussed in Katharine’s science class.