Duck Pimples(1945)

Donald has an unpleasant evening when a mysterious book salesman comes to his door then disappears leaving Donald with a collection of whodunnit novels. He reads one and gets so fully involved in it that it appears that the characters are actually coming out of the book and into his living room getting him involved in the murder caper. Finally the author of the book, J. Harold King, steps forth and claims Donald innocent. The characters return to the novel from whence they came leaving Donald wondering if it was really just his "imagination"