Shocks for the Chalet School (by Elinor M Brent-Dyer)

In my gradual re-reading of the ‘Chalet School’ series by Elinor M Brent-Dyer, I reached ‘Shocks for the Chalet School’, 25th in the original series. I hadn’t read it since 2012, when I had an abridged Armada edition only. I was given a hardback by a relative who was clearing out someone’s attic, and out of curiosity, compared the two (off and on) as I read. I hadn’t recalled any of the plot. 
The story opens as Miss Annersley, Head of the Chalet School, receives a cable from Australia. That’s...