Early in this film, a circus owner (Marjorie Main) is given custody of her sister's young daughter after the sister dies. Soon, the little brat burns down the circus and instead of beating the snot out of the kid, they celebrate because now they can make an insurance claim! I don't think insurance works that way and this seems like a rather dubious message to be passing on the the audience...but, after all, this is a rather dubious sort of film.
Years now pass following the fortuitous fire. Now the little brat has grown and is a star on the trapeze. I agree with another reviewer who hard a hard time accepting that she is, according to Main, "the world's greatest aerialist"! She was a lot better than me or my dog, but seemed far from the greatest. But, the actors in this film try their best to pull off the idea that she is terrific--as evidenced by the men who are smitten by her. What happens next is rather unexciting--as can be said of just about every circus film of the era. Dull writing, acting and action spell the recipe for a very sluggish film.
And, speaking of dull circus films, this genre has apparently died--thank goodness. Despite winning a totally undeserved Oscar, "The Greatest Show On Earth" was an amazingly dull film whose only advantage over "Under the Big Top" was a glossier look and bigger budget. "Circus World" was likewise very big and glossy--but even duller. About the only circus films that WERE worth seeing were films like "Circus of Fear" and "Berserk" because at least they were meant to be trashy horror films--not trashy and horrible films like the rest! By the way, this is yet another film with a supporting role for a black actor known as 'Snowflake'--a rather demeaning stage name for a man--more like a name you might expect for a trained animal. It's a sad sign of the times in which it was made. Other such ill-named black actors of the era included Farina, Buckwheat, Sleep 'n' Eat, and, of course, Steppin Fetchit. My how times have changed!