
The posthumous papers of Rebecca MacKenzie document her adventures, along with her brother Doug, in 1920s China as the teenaged siblings are sent to live aboard their uncle's ship where they become involved in the dangerous activities of a mysterious secret society called the Honourable Guild of Specialists.
http://www.amazon.co.uk/Operation-Red-Jericho-Guild-Speciali...
Can't find a reference to The Ambassadors, but maybe that just doesn't turn up in the reviews.
Thanks for the pointer.
Edit: Found it - it's mentioned here:
http://goodtoread.org/initial/o/operation-red-jericho/
Great review.
