Re: Plot
Originally it went from London to Istanbul via a cross-channel ferry. At one time, it shrank down until it just did Paris to Vienna but that was way after Agatha Christie's time.
There was also one train company that ran (as a one off to show it was doable) train journeys from London across the channel to Paris, Berlin, Warsaw, Moscow, then via the Trans-Siberian Railway to Irkutsk, then Ulan Bator, Sian, Peking (as it was then), Shanghai and ended in Hong Kong. (Apparently it took about six weeks).