Amongst the many duties which fell to the care of Bertha Keys was the one of looking after the postbag.  Every afternoon she took the girls' letters and put them in that receptacle, hanging the key on a little hook in the hall.  Morning after morning it was she who received the postbag, unlocked it, and brought the contents to Mrs. Clavering, who always distributed the letters herself.  Thus it was easy for Bertha to abstract the letters which contained the Dawlish postmark.  She did this for a reason.  It would never do for Florence to find out that her mother had not received the letter with the postoffice order.