GoodReads meta-data is 223 pages, rated 4.22 by 120 litizens.
Genre: krimi.
Verdict: Diverting.
It’s 1898 and Watson has been kidnapped by a criminal mastermind (no, not him) in a plot to start a European war. His rescue is facilitated by his niece, Lucy, and Sherlock. Oh, and the latter’s smarter brother. There is rich period description of the Orient Express. The plot is as complicated as one could want. One distinction is the evident corruption, not mere incompetence, of the London police.
This is number seven in the series heretofore unknown to me.