This is my top favorite out of the "Pearl Pureheart/Oil Can Harry melodramas," which became the most common plot for some Mighty Mouse cartoons.
You know, I thought this cartoon was the first of those melodramas, but it is actually the third one. In this cartoon, Pearl's name was changed to "Little Nell" and she performs in the circus as a trapeze artist. But Oil Can Harry seeks her hand in marriage, and foiling the feline cad is (as the title says) a mysterious trench coat-wearing stranger. Who is he? You'll have to find out when you watch this cartoon.
I'm sorry to say that I have nothing else to say about this cartoon, other than I love it. I thought the story was decent and the animation perfect.