Hitchcock is a master of the everyday-man wrongly suspected of a crime scenario, but here we're looking for clues that Charlie's a wrong 'un. Quick to pick up the trail is his adoring niece, played by Teresa Wright, who's so close to her uncle she's known as 'young Charlie'; she even believes there's an extrasensory link between them and he's come to town precisely because he sensed she was bored.
Young Charlie's sharper than the rest of her family - including dad, who discusses amateur criminology with his neighbour, a young Hume Cronyn, and is taken in by the gift of a watch - but also smitten with her uncle. The interest is reciprocated, but it's only when one of the detectives falls for her that the case begins to fall into place - when Uncle Charlie gives his niece a stolen ring in a cod wedding scene.
Much is made of the film's small-town setting - Thornton Wilder worked on the script - but I particularly like the opening scenes in Philadelphia, which so cleverly set up Uncle Charlie's character, and are filled with rundown fire escapes and desolate city streets that presage the start of Psycho seven years later.
Best of all is the sense of restrained, almost insouciant, menace in Cotten's performance. This was a year or two after Orson Welles had cast the stage actor - and one-time theatre critic - in Citizen Kane (1941). Cotten made his name as a romantic lead but this is one of his most compelling performances - his slyness contrasts nicely with the character he was to take on in Welles's The Third Man (1949).
When he's found out, Hitchcock even gives Cotten a speech to match Welles's famous outburst atop the ferris wheel in Vienna. 'The cities are full of women, middle-aged widows,' Charlie tells his niece, 'husbands dead, husbands who've spent their lives making fortunes, working and working. And then they die and leave their money to their wives, their silly wives. And what do the wives do, these useless women?
'You see them in the hotels, the best hotels, every day by the thousands, drinking the money, eating the money, losing the money at bridge, playing all day and all night, smelling of money, proud of their jewellery but of nothing else, horrible, faded, fat, greedy women... Are they human or are they fat, wheezing animals, hmm? And what happens to animals when they get too fat and too old?'
There's a great piece of mathematical business in Shadow of a Doubt ('1888! Fifty-three years ago') that places the action on the eve of the USA's entry into World War II and it's initially tempting to suspect Uncle Charlie may be a Nazi spy; he's unwilling to have his picture taken, mysterious about the source of his money - and his sister, the sweet-as-apple-pie matriarch, seems too good to be true. Even her efforts to place Charlie in their family history seem suspicious.
Made just two years after Saboteur, which makes the link to Nazi spies explicit, it's easy to imagine these siblings as German sleepers, only that the sister's gone native and settled into her hometown life. It's masterfully done - full, as the title would lead you to believe, of brilliantly shot shadows, notably on the landing outside young Charlie's bedroom, where much of the action takes place.
Six years later Max Ophüls visited small-town America for The Reckless Moment. This is a less-innocent world - closer to the big city - where reputation is all. This time the mother (Joan Bennett) does try and protect her child, by covering up the death of her daughter's no-good boyfriend. There are lots of stairways again.
In both films, it's left to the women to get the better of their tormentors - the threats to their family lives. Hitchcock thought Shadow of a Doubt the best of his American movies, and who am I to disagree?