Blondie's Lucky Day is a 1946 American comedy film directed by Abby Berlin and starring Penny Singleton, Arthur Lake, Larry Simms, Marjorie Ann Mutchie.

Mr. Dithers has a client, a land-developer, who wants to build a theater—and Dagwood's new hire develops a set of design blueprints for the project.

While the developer departs into his adjoining "gym", for a massage, the son remains for a while, lounging in his father's office.

The office secretary arrives in the gym to find Dagwood standing over three seemingly-dead "victims," and calls police.

(Spoiler alert: the next paragraph reveals the ending) The developer realizes that the "Bumstead Construction" blueprints are superior to those of his buddy, Mr. Dithers—creating a quandary for him: loyalty or quality?