The Vitamin G-Man1943

A detective in training is about to take his final exam. He is sent to room 13, where his professor befuddles him with a tricky doorknob. Next, he goes to a tea party with his professor loosely disguised as an old lady; the butler serves a pot of "T.N.Tea" even though his back is full of knives. The professor keeps disappearing; the student tracks him by his footprints, even though the footprint powder at one point becomes train tracks and the doors he opens have a skeleton and some card-playing ghosts. Finally, the budding detective phones for the police; when they arrive (driving on the phone lines) and pile into the phone booth, he passes, and is given the first, second and (under bright lights) third degree.