Footnote:

Think for instance of Umberto Eco's The Name of the Rose. In order to enter the secret room in the library where the master murderer is hiding, William of Baskerville tries to unlock the mystery behind a Latin sentence that he has read in a manuscript note left by one of the killed monks: "Secretum Finis Africae Manus Supra Idolum Age Primum et Septum de Quatuor". It is only at the end of the plot, however, following an incidental remark of his assistant Adso, that William realizes the big mistake incurred throughout in translating this sentence. The secret of the Finis Africae is not revealed by "the first and seventh of the four", as he mistakenly thought thus far, but by "the first and the seven of Quatuor" (i.e., of the word "four"). A minor problem of correct Latin declination. Thus, they could go to a mirror with the apocalyptic sentence engraved over it, "Super thronos viginti quatuor". When the letters Q and R were simultaneously pressed, as suggested by the solving formula, the door to the secret chamber was open.

Calculating the Limits of Poetic License:
Fictional Narrative and the History of Mathematics
Leo Corry - Tel Aviv University