Charlie Chan (Warner Oland) takes his wife and twelve children on an outing to the circus after they receive a free pass from Joe Kinney (Paul Stanton), the owner. In actuality, Joe wants Chan to discover the source of certain anonymous, threatening letters he has been receiving. As the Chan family continues to accompany the circus on their tour, Charlie makes progress in his investigation amidst venomous cobra attacks, Joe’s eventually death from a rampaging gorilla who mysteriously escaped his cage, and Chan’s eldest son romancing the traveling contortionist. As Chan digs into Joe’s past, he discovers a paper trail of forged documents and fake deals, which convolutes the case and creates a scenario beyond a simple whodunit.