: It provides a more poignant look at Hastings' post-war trauma (the "thousand-yard stare") which was less emphasized in the book.
: It famously uses floor plan diagrams and in-text evidence (like chemical prescriptions) to help readers follow the investigation like a game of Clue.
: Unlike other Poirot episodes that were shifted to the 1930s, this adaptation stayed true to the 1917 setting to capture the atmosphere of World War I.