When the circus comes to town, a clown and his monkey get into trouble

Kid detectives Brian and Sean Quinn are on their way home when they see a clown causing a commotion outside the mall. The Star-Spangled Circus has just rolled into town, and Crackers the clown and his faithful monkey are there to promote it. But just as Sean is about to get a good look at the monkey, it escapes its collar and runs off, leading a frantic chase through the mall. and while the primate runs wild, someone uses the distraction to rob the stores. To the Quinn kids, it looks like this clown is pretty serious—about crime.

But that night, the clown's son asks Brian and Sean to help him prove that his father wasn't even at the mall, and that the stores were robbed by an imposter. To get to the bottom of this big-top mystery, the Casebusters will learn that under their makeup, not all clowns are smiling.