Ballyhoo (1985), a circus mystery by Jeff O'Neill.
As described on the box:
Spangleland! Sawdust and glitter, buffoons and cotton candy! It's a place where your wildest dreams can come true! At least, that's what you think...until you get behind the scenes at the big top. Then you learn how easily sweet dreams can turn into nightmares.
Beyond the spangles lies a seedy world of deception and crime. Exploring the tattered corners of the circus lot, you overhear a conversation about the owner's daughter. It seems she's been kidnapped, and the hired gumshoe couldn't find the nose on his face. Good samaritan that you are, you start poking around on your own.
But watch your step. As the night progresses, you realize you're in as much danger as the little girl. For the kidnapper is lurking right there on the lot, trying to set you up for a permanent slot in the freak show.