Once again, Portuguese auteur Miguel Gomes delivers a film in which the most complex sophistication coexists with innocence and charm. It is at once very worldly and yet unworldly – in fact almost childlike at times. It is elegant, eccentric and needs some time to be indulged. The British characters are played by Portuguese actors speaking Portuguese, except for a few rousing choruses of the Eton Boating Song, which is in English. (There is more literal casting for other nationalities.) And yes, it is six parts beguiling to one part exasperating. But quite unlike any other film in the Cannes competition, it leaves you with a gentle, bemused smile on your face.

The story, co-written by Gomes, could be adapted from something by Somerset Maugham, but is in fact an original screenplay. (I was also reminded of Jane Gardam’s colonial novels or Evelyn Waugh.) In colonial Burma during the first world war, Edward (Gonçalo Waddington) is a minor British functionary in Rangoon, unhappily waiting for the arrival of the London boat, on which is the woman to whom he has for seven years been engaged: Molly (Crista Alfaiate). But Edward gets cold feet and before Molly arrives, he flees to Singapore, where he runs into his fiance’s rackety cousin in the bar of the Raffles hotel, and allows this seedy and excitable man to believe that his own extraordinary, furtive behaviour has something to do with spying.

Living like a hobo, Edward goes on to Bangkok, Saigon, Manila and Osaka, from where he is expelled by Japanese authorities for his suspected connection with US naval intelligence. Then he goes to Shanghai, Chongqing and Tibet where he sees pandas in the trees and meets an opium-addicted British consul who tells him the empire is finished and that westerners will never understand the oriental mind. But the formidable Molly is hot on his trail and not to be deterred.

The movie’s first half is Edward’s perhaps rather somnolent story but the second half belongs to Molly’s more eventful, even sensational quest narrative. We have time to get to know this complicated, determined woman with her odd, spluttering laugh and a predisposition to faint in public which may be epilepsy. The voiceover narration is in the various languages of each of the places the story is set and, in keeping with Gomes’s docu-realist approach to fiction, the tale is interspersed with scenes of the modern-day cities in which each scene takes place. These are a framing device, partly, but Gomes might almost be playfully suggesting that these documentary scenes are the film’s whole point and it’s the story that should be in the background. They are largely in colour, whereas the story is in black-and-white – but this isn’t a hard-and-fast rule. And in fact, though there is a good deal of “documentary” footage in the first half, the Edward half, Molly’s half of the film is almost all story – which, it should be said, gives the movie a welcome energy boost.

Grand Tour looks to be a romantic, extravagant and comic epic – with some accumulating suspense as Molly begins, against all odds, to catch up with her timid fiance (who clearly doesn’t deserve this remarkable woman.) Are we going to be treated to a gorgeous reunion of lovers? Well, maybe that’s how David Lean would play it and Lean would have made much more of the scene where Edward meets the Thai crown prince at an official reception. (It’s a comparison that has already occurred me here in Cannes for the competition’s other Asian sundered-lovers drama, Jia Zhangke’s Caught by the Tides.) Gomes of course approaches it far more obliquely: there is melancholy and a feeling that the world is a big and confusing place in which individuals can get lost and their hopes and dreams come to nothing. We are left with a poignant farewell, and a self-aware gesture at the idea that this is a fiction, so we shouldn’t be too sad. Grand Tour is a unique and valuable experience.