Valuable works are boldly stolen from the museum of art one after another, and the criminal leaves encrypted messages every time. Shrewd Inspector Meguro, his sister - mathematician Rika, and erudite journalist Yoneda Rio challenge the daring kidnapper, but for this they need to solve the riddle of the cipher. The book will acquaint the reader with the general concepts of cryptology and its underlying interesting mathematical laws, as well as with how cryptography is used in our daily life.