Dagwood accidentally invents a non flammable paint. Con men visit Blondie and, while her back is turned, switch cans of it for ordinary paint, hoping to have the special paint formula analyzed. Dagwood unwittingly paints his boss Mr. Radcliffe's barn with the wrong paint as a test; and with Mr. Radcliffe watching, sets the barn on fire, only to have it burn down, disgracing Dagwood. Blondie then, using an assumed name, is hired as a secretary in the con men's office, where she records their incriminating conversation. As she is about to leave and take back Dagwood's valuable paint, they seize the paint and tie her to a chair as prisoner, but she is soon rescued by a visitor. She rushes to Mr. Radcliffe's office, where the con men are in the process of selling him Dagwood's nonflammable paint, which they claim is their invention. She then plays the incriminating recording, exposing them and having them arrested.
