The script fairly crackles and the pace is nearly relentless until the protagonists arrive at the inn for the night. It’s jumping from trains, man hunts across the moors and enemy agents turning up everywhere. The dialogue is sexy by 1930's standards, reminiscent somehow of Bacall and Bogart in The Big Sleep - the electricity between Carroll and Donat is a joy to watch. It's all innuendo, of course, which is far steamier than being explicit about things - but I bet it initially troubled the censors all the same. The acting too is top-notch and some mention should be made of Dame Peggy Ashcroft (looking sexier than Carroll in my view) in an early role. Donat is superb as a kind of proto-type James Bond, all debonair and very, very English.
The film may not have the budget or the scale of some of Hitchcock's later work but there's no doubting his way with a story. We have to remember than this movie was made 70 years ago and in context is full of violence sex and a roller cosater ride! We are right into the thick of the story within about three minutes of the opening titles and it never lets up.