Impulsive 15-year-old Marjorie Anderson starts at the ridiculous girls' school of Brackenfield, where deportment is everything and the staff reads your mail as a matter of course. This takes place during the Great War, and so knitting socks for soldiers is also a part of the school curriculum.
And from there on we get intrigue! German prisoners of war! not-even-subtextual-anymore lesbianism! spies! misunderstandings! more knitting!
The low point of the book is a little boy that Marjorie and her sister befriend, who is chronically ill. Nothing wrong with that, except the boy is obsessed with fairies and so teeth-rottingly twee I need a new filling. It was also a little too easy to guess the book's central mystery, which wasn't even introduced until somewhere around the midpoint of the book.
I was still entertained!