Notorious is perfect. Everyone knows that. It's a testament to Ben Hecht's complex, headlong script that so many people have tried to rip it off and a testament to Hitchcock's genius that no one has ever succeeded. Take a look at the gabby, inconsequential, forgotten Mission Impossible: II and you'll see what I mean. The more obvious glories of Notorious include a revelatory performance from Cary Grant as the morally exhausted American agent Devlin, a terrifying Nazi-mother super-villain played by Leopoldine Konstantin and cinema's most cunningly prolonged kiss.

According to the Hays censorship committee, no on-screen kiss could last longer than three seconds. So Hitchcock had Grant and Ingrid Bergman kiss for two seconds, then break, nuzzle and start again, until he had three minutes of highly charged smooching. Watching it, it's impossible to believe that an assistant director with a stopwatch was just out of shot yelling: "OK. Lips … and … stop."

The film also includes one of Hitchcock's most famous shots, when the camera plunges over the bannister of a high staircase into the glitter and bustle of a party, shimmies through the guests and comes up behind Bergman to find a key hidden in the palm of her hand. The shot goes to the heart of Hitchcock's aesthetic – which is all about control. Notorious gets its unremitting suspense not from tooling up the bad guys or sending in the helicopter gunships but from narrowing the focus so that the opening of a bathroom door shakes you like an earthquake and a stolen glance burns you like a ray gun. As Truffaut said, it "gets the maximum effect from the minimum of elements".

You can see this in the mileage Hitchcock gets out of bottles and drinking in this film. The first time we see Bergman's Alicia, she is drunk. When she gets together with Devlin, they buy a bottle of champagne, but it stays unopened when their celebration is cut short by the arrival of her orders. At the climax of the film, Alicia – who has been trying not to drink – has to ensure that the wine flows so freely that she has a reason to go down to the wine cellar where "the MacGuffin" (plot device) is stored. Montages of bottles and glasses reappear like a musical theme.

But the film's real triumph is its emotional and moral complexity. Devlin headhunts Alicia and then falls in love with her. Alicia is the "notorious" daughter of a Nazi spy. Her disgrace makes her ideal bait for the honey trap that Devlin has to set for Alexander Sebastian (Claude Rains), the linchpin of a group of escaped and unrepentant Nazis hiding in Brazil. So Devlin is a good man, on the side of right, who pimps out the love of his life. Sebastian, on the other hand, is a Nazi who truly loves someone. A great artist – Michael Haneke perhaps – might create and explore these moral contradictions. Only Hitchcock could milk them for tension.

When Sebastian's mother discovers the truth about Alicia, for instance, she poisons her. Alicia therefore fails to make her meeting with Devlin. He can interpret this in two ways – either Alicia is in danger or she has fallen for Sebastian. The next twist thus turns not on a piece of information or action but on whether Devlin's jealousy is stronger than his love. It's both heart-racking and sickeningly tense.

People tend to be dismissive of Hitchcock's MacGuffins. In Notorious, though, the MacGuffin deftly amplifies and deepens the moral resonance, implicating the whole western world in its twisted emotional drama. Because the MacGuffin here is a cache of uranium, hidden – of course – in wine bottles. The film was released within months of the dropping of the atomic bombs on Japan, an act that reflects the moral ambivalence and apparent necessity of Devlin's pimping of Alicia.

Hitchcock is the great Catholic artist, returning again and again to the themes of the fallen nature of creation. Sometimes – The Wrong Man, The Birds – this comes out as a bleakly thrilling feeling that everyone is guilty. In Notorious, however (and in Shadow of a Doubt, Psycho, North by Northwest and Vertigo), it plays the opposite way – that the world is fallen and therefore the best are only different from the worst by the grace of God; that our worst failings are forgivable and repairable; and that no matter how compromised we are, we can – and must – love one another. It's the reason his great thrillers are also great love stories. It's the source of the power of that last shot – a hungover pietà – of Grant carrying Bergman out of the house of shadows and into the possibility of love.