This movie is pure Bulldada. And that's pretty awesome. The first half is the actual story, while the second half is a series of bands showcased, including Frankie Lymon and the Teenagers doing "(I'm Not A) Juvenile Deliquent" (which must be heard – and I think it was actually a minor hit!).
Anyway, in the first part, a girl needs to get a new dress to go to the Alan Freed Rock Concert (history, sadly knows Alan Freed less of the Rock'n'Roll Pioneering DJ and more as the Guy Who Took Payola), and gets a job – though it's not working out as well, so her greatest rival offers to loan her the dress money at 100% interest. She accepts and buys the dress, only to find out that the rival demands the money the night of the show, meaning she can't go because she'll have to work off the debt, as she only has the inital amount sans interest. In fact, she's shocked to learn the interest is so high – she thought "100%" meant "100 cents", or "One Dollar"! Not Twice the Amount! Uh-oh! So, she calls her father in tears, who confronts the rival and informs her of usury laws and etc, bails her out, and they all get to see the Rockin' New Acts! And the day is saved!