Picky
I have the feeling Agatha Christie never took a boat to Canada or a train to Alberta. When I was five I sailed from Quebec City to Le Havre and it took a week. These days it's three days travelling time from Quebec City to Banff not counting waits and inevitable train delays, and I fancy that ninety years ago the trains were a lot slower. Certainly in 1974 it took me three days just to get to Saskatoon.
So if in the 1920s you have three weeks to track down a witness in Banff before a man is hanged for murder, and you're leaving from London and travelling by boat and train, I *really* don't think you're going to make it.
So if in the 1920s you have three weeks to track down a witness in Banff before a man is hanged for murder, and you're leaving from London and travelling by boat and train, I *really* don't think you're going to make it.