This element of surprise or mystery — the detective element as it is sometimes rather emptily called — is of great importance in a plot. It occurs through a suspension of the time-sequence; a mystery is a pocket in time, and it occurs crudely, as in "Why did the queen die?" and more subtly in half-explained gestures and words, the true meaning of which only dawns pages ahead. Mystery is essential to a plot, and cannot be appreciated without intelligence.
E. M. Forster