The Secret of Galleybird Pit (by Malcolm Saville)

Having re-read the ‘Lone Pine’ series by Malcolm Saville for the umpteenth time, I decided to read some of his lesser-known books for children, which have been on my shelves for decades. I picked up ‘The Secret of Galleybird Pit’, with no memory of the story. According to a note in the front of the book, I bought it in May 1974 for the sum of 17.5 pence. I assume I read it then, but as far as I know, I have not re-read it in the intervening forty-nine years. 
Lucy, who is twelve, and her broth...