read someone like an open book, to

To discern someone’s thoughts with great accuracy. The analogy of a guileless person to an open book was made by Shakespeare. “Read o’er the volume of young Paris’ face,” he wrote in Romeo and Juliet (1.3), and again, “O, like a book of sport thou’lt read me o’er,” in Troilus and Cressida (4.5). A closely related turn of phrase is to read someone’s mind, which dates from the late nineteenth century.