Probably these type of movies destroyed Gloria Jean - and here she didn't even get the chance to sing - except one song.
Wendy lives with her uncle, in a second-hand goods/ pawn shop - or rather in her fairy tale lands - the bed-time stories her uncle told her, and probably even then, in her teen-age. Along with the fairies and the princes, of course there were demons/ witches, which she, in her imagination, lived in the dark storage cellar of the shop. The uncle, understandable, was extremely protective of her, and kept her away from the street-gang, led by Johnny, strangely, seemed to be the only one of the age who could have romantic interest, towards her, all other of his group of friends, looked to be quite a few years too young. May be he was the only of the age group who had to stay back, while other went to college ?
On a dark night, a strange and menacing man came to the shop, to pawn a Stradivarius violin- which the uncle keeps in a safe place - his cellar, whose key is always kept by Wendy (so that the demons can't come out?). But then, at night Johnny comes over while uncle is away - and before the uncle came back, he has secured the violin, and played some, not very consonant, notes on it for Gloria to sing. The Uncle is back. The highly protective Uncle should be quite angry at the young man spending time with his minor niece, but that wasn't expressed, and rather a wrong piece of history - of Antonio Stradivari's wife eloping with his friend was told. I wonder which wife's character was assassinated ? The first one was a widow before marriage, thanks to her brother in law, who killed her first husband, but spared the second, Anton, so when she died, she was still wedded and with Anton. The second one became widow. There was no mention of any third, or even affair. Was it to scare the two young ones? May be, but Johnny knew of Stradivarius, so a bluff won't have been so easily digested.
Then onward the movie went through a series of - too predictable cliches - till the end. Including the famed but mysterious villain was easy to guess.