Books are a source of knowledge, a pleasant pastime and even the discovery of secrets, but sometimes the sale of books itself can be of interest to law enforcement agencies. As it happened in Mysterious Bookseller. Detective Mary is investigating an interesting case involving a bookseller. He sells rare publications and prefers to do it bypassing the law so as not to pay taxes, moreover, his goods may not be obtained entirely legally. His identity is mysteriously hidden; no one has personally met him. Even those who sold him books and who bought him. Everything happens through intermediaries, but when the police get involved, everything comes to the surface. Help the detective solve the criminal in the Mysterious Bookseller and bring his black deeds to the surface.