December 1917. An important visitor arrives at a field hospital not far from the front, who makes sharp deductions about the way the ward is run based on small details that he sees. Sherlock Holmes is apparently only present for a tour, but asks searching questions about a young officer who apparently died in the hospital, but whose records have mysteriously vanished. As Holmes digs deeper, details emerge pertaining to a cover-up that stretches from the trenches to the top of the War Office, and conspiracy on both the British and enemy fronts.