Circus Caper

A boy named Tim and his little sister Judy go to a circus. They want to buy tickets to enter the circus, but they only have money for one ticket, so only Judy goes in. After the show, the boy is at the exit to meet Judy when she comes out, but when she doesn't the boy sneaks into the circus to rescue his sister from the ringmaster Mr. Magic who has taken her hostage. (mobygames.com)