After the "Snobby hatte Shoppe" closes for the night, a mouse comes out of his hole and looks to see if the coast is clear. He turns on the lights and then calls his other mouse friends out to party. His girlfriend leaves the hole last, watched by a jealous rat. When the couple takes a break from dancing, the rat kidnaps her. Her boyfriend rallies his friends to find her. The mice under each type of hat in the store adopt the personalities the hats suggest, such as farmers, firemen, or soldiers. A "blind" mouse points the way to the kidnapper and the hero saves his girlfriend. The face shield of a knight's helmet serves as jail bars for the rat. Soon our happy couple marries, wearing an enormous top hat and veil.
"A Sunbonnet Blue" was the final 1930s cartoon to have stock music playing on the ending titles. All subsequent cartoons ended with the "Merrily We Roll Along" theme.
The original Blue Ribbon ending title is currently lost due to the 1995 dubbed version being released on LaserDisc. No print with the original Blue Ribbon ending card has ever been released on home video.