The class in room 3B knows a secret teacher 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 schook, but when the discover Harry's pet cat, Goog, has hitched a ride in Grandma's truck. They have to catch him before anyone else does. They chase him all over the school - even into places students (and cats) aren't allowed to be. Will the boys capture Goog without being caught themselves? Or will Harry's cat get him into the most horrible trouble ever?