One of the greatest films of all time, and erotic too! Truly this is one of the top ten greatest films ever made. One very interesting element that makes it incredibly modern is how erotic it is. Yes it is a spy thriller/mystery, but what keeps the film so timeless is its massive sex appeal, something which was all but forbidden at this point in American films. Robert Donat successfully projects the image of a sensitive but nevertheless attractive man who shows believable and genuine affection to the three women he encounters in the film (which in all three instances involve misconceptions and eating).
The first sexual reference is the fact that the film opens at a music hall, where a Mr. Memory refuses to answer a question about the age of Mae West (need I say more?). Here he meets a mysterious woman who, without even getting each others names, asks for him to take her home with him. Although nothing actually happens between them, he is incredibly kind to her even though he doesn't believe her until she gets killed, he thinks it is just persecution mania at first. He both gives her a drink and feeds her (haddock specifically). Notice that when they enter the kitchen, he closes the door behind him and lights up a cigarette, then walks around to her and leans back against the stove. He then butters the bread that he gives her. He cuts the bread with the same knife that is ultimately used to kill her. When she dies she falls directly on top of him sideways.
The next morning he escapes his building by telling the milkman a story about having an affair with a married woman (whose brother and husband are supposedly outside), but only after he first attempted to tell the man the truth and failed to get a reaction out of him. This is an interesting instance in which a man helps him (this never happens again until the very end of the film) and he accomplishes it by making up a sex story.
He ends up in Scotland and pays a farmer to stay at his house overnight. He meets the mans wife, a much younger woman who Donat initially thinks is the mans daughter, and the husband ends up thinking that his wife is planning on committing adultery with the stranger (he leaves after saying grace and watches from the window as the two converse about the murder charge, thinking it is love talk). The husband eventually catches them in the middle of the night, thinking they are about to run off to make love but eventually realizes that Donat really is just running from the law. When he leaves he kisses her on the cheek, and it is implied that she has developed feelings for the stranger in the few hours they have known each other.
Finally, there is the more developed relationship with the Madeleine Carroll role. They first meet on a train to Scotland and he kisses her in order to try to avoid getting caught by the police. A writer for The New Yorker claims that in a way the Donat character is trying to convince her that what he is about to say is the truth by letting her taste it first. She doesn't buy it and tries to help the police in catching him. The next time they meet is at a political rally during which he engages in a brilliant and charismatic speech about left-wing politics. They end up handcuffed together, go to an inn, order a room under which they sign as husband and wife, eat sandwiches, and sleep in the same bed for a while (he also says damn to her three times). Notice that he knows what to do when she takes off her stockings, which have gotten wet earlier, he even hangs them up for her in front of the fireplace. There is something about the way the two act with each other, their chemistry, which implies at the very least that they got along well (an off-camera friendship could explain this).
Ultimately it is as much the dominant performance of Robert Donat as it is the direction of Alfred Hitchcock that make this film immortal. From 1935 to 2019, it has aged well, if at all. Truly one of the greatest films ever.