Some write so that people will certainly read and understand them, even after a thousand years, others - so that a single addressee can read, and for the rest the message would remain a secret. The book, which was first published back in the 30s of the XX century, included 15 action-packed scientific essays devoted to the eternal, but not often covered topic: decoding ancient letters (Egyptian, Etruscan, Orkhon, Siberian and others), as well as messages - military, underground workers, diplomats of the past.