Robert Michael Ballantyne 
Post Haste (Annotated) [EPUB ebook] 

‘Post Haste’ is a fascinating story by prolific children's author R.M. Ballantyne, set during the early days of the general post office. Still in its infancy, sending a letter through the post office was not yet a guarantee of its’ safe arrival. When several highly sensitive and important letters to the same addressee all go missing however, is there more to it than meets the eye? Philip and his sister Mary Maylands, along with their friend George Aspel are soon on the case, as they attempt to get to the bottom of the mystery.