Errol Flynn in an operetta? Yes please! Errol Flynn singing? Apparently, not in this one. You only have one chance to hear that, in the cute variety show Thank Your Lucky Stars. In this one, all the singing and dancing are done by Anna Neagle and Patrice Wymore.
As quick as I am to recommend all of Errol Flynn's movies, (because him in a lousy movie is better than nothing) I'm not going to recommend you watch this one. If you didn't like seeing him playing a no-account drunkard in The Sun Also Rises, you're really not going to like seeing him in this movie. There are a few scenes where his character is drunk, and he's so convincing, I had to wonder whether or not such a state was actually written in the script or if it had to be adopted to suite him. Also, since Patrice's character is supposed to have loved Errol from afar for years, and she carefully looks after him, it adds another layer of sadness. In real life, Patrice and Errol were married, and she put her career on hold to look after him towards the end of his life.
If you do want to watch it, here's a quick summary of the plot: Queen Mother Martita Hunt informs her playboy son that his father has died and he's going to be coronated King soon. He must return to his own country and drop his mistress, Anna Neagle, he's been with for years. While he enters into an arranged marriage for the sake of his kingdom (with Patrice) he continually pines away for Anna. Since Patrice has loved him for years, there's a whole bunch of unrequited love in the story. This isn't a light operetta, but instead one that's quite sad with every main character battling heartbreak.