Mrs. Jewls recruits Calvin, who has a "big, round face" (7.1), to deliver a message to Miss Zarves on the nineteenth story. There's only one problem with this request: At Wayside School, there is no Miss Zarves. And the nineteenth story doesn't exist. (Okay, it's technically two problems—no such teacher, no such floor.)
This doesn't seem to bother Mrs. Jewls, who tells Calvin he'll go home early unless he delivers the message; the other kids laugh as Calvin leaves the room. Of course Mrs. Jewls has also neglected to give him the note. "I'm supposed to take a note I don't have to a teacher who doesn't exist, and who teaches on a story that was never built," Calvin thinks.
Calvin walks up and down between the eighteenth and twentieth stories of the building, but he can't find the nineteenth. It's just not there.
He decides to go to the administration office and leave the note in Miss Zarves' box, but he finds that she doesn't have a box. He decides this is okay, because after all, he doesn't have a note.
Calvin decides to go find Louis, because "Louis will know what to do" (7.27). He finds Louis playing basketball and explains his problem. "It's very simple," Louis answers. "You are not supposed to take no notes to no teachers. You already haven't done it" (7.40).
Calvin and Louis decide they have no idea what Louis just said, but Calvin goes back to class anyway.
Mrs. Jewls praises Calvin for delivering the note when he gets back to class. The other students have no idea how he did it. Mrs. Jewls says the note was very important, because she "told Miss Zarves not to meet her for lunch" (7.51). She rewards Calvin with a Tootsie pop.
Calvin thanks her and says, "it was nothing" (7.54)—which is exactly what it was.