Horrible Harry's class knows a secret party is happening in the library—Harry's grandma even baked a special cake for it. But who is the party for? Harry and Doug plan to find out after school, but when they discover Harry's pet cat, Googer, has hitched a ride in Grandma's truck, they have to catch him before anyone else does! They chase The Goog all over school—even into places students (and cat!) aren't allowed.Will the boys capture The Goog without being caught themselves, or will Harry's cat get him into the most horrible trouble ever?