Poirot has slightly more time to look for the lost Prime Minister in the episode, given that he meets Lord Estair and Sir Bernard Dodge at the Foreign Office at noon rather then the two men arriving in his rooms in the evening.
In the story, Poirot follows the Prime Minister's trail to Boulogne and crosses the English Channel. In the episode he doesn't even leave England altogether.
The Greater-Scope Villain of the story was Frau Bertha Ebenthal, a German spy who posed as Commander Daniels' sister. In the episode, her role is taken up by Commander Daniels' wife, who is a member of an Irish freedom fighter group.
Miss Lemon appears in the episode while being absent in the original story.
Adaptation Expansion: The episode also includes a subplot of Poirot being fitted for a suit, and refusing to acknowledge that he has put on too much weight for the previous year's measurements to fit him.
Adaptation-Induced Plot Hole: The switch to the kidnappers of the story being pro-Irish rather than pro-German introduces a slight anachronism, as Irish independence had been granted thirteen years before the episode takes place. This necessitates an extra motivation on the kidnappers' part: allowing Germany to re-arm so Britain is distracted and can't meddle in Irish affairs.
Better to Die than Be Killed: Mrs Daniels chooses to shoot herself rather than be arrested, tried, and executed after the police corner her and her group.
Bound and Gagged: Commander Daniels claims that he woke up like this, though it's later revealed to be a fake-out. Also, toward the end of the episode, Prime Minister MacAdams is tied up like this by the Danielses.
Foreshadowing: When Poirot meets Imogen Daniels, she's shown standing in front of a harp that looks very similar to the harp depicted on the coat of arms of Ireland, signaling her true allegiance.
Gory Discretion Shot: Mrs. Daniels' suicide isn't shown on camera, only some blood spray on a nearby stone and the camera "falling" to the ground, imitating her body's fall.
Setting Update: The episode is notable for one where the series being set in the 1930s informs the entire adaptation.
Instead of the Prime Minister departing for Europe for a peace conference in the closing days of World War I, the Prime Minister instead heads to Europe for a summit meant to prevent the further rearmament of Nazi Germany.
The antagonists are changed from a German spy and their accomplices to a cell of Irish freedom fighters.
