The plot of Nicholson Baker’s debut novel is simple: A man, returning to his office building from a lunch hour that included milk, a cookie, a small errand, and a stroll, goes up an escalator. That’s it. Only 135 pages long, and graced with numerous lengthy and absorbingly digressive footnotes, this is a wise, patient exploration of that unseen mental space in which we pass our time—and it’s very funny to boot