Young journalist Tintin and his dog Snowy are browsing in an outdoor market in Brussels, Belgium. Tintin buys a miniature model of a ship, the Unicorn, but is then accosted by Barnaby and Ivan Ivanovitch Sakharine, who both unsuccessfully try to buy the model from Tintin. Tintin takes the ship home, but it is accidentally broken, resulting in a parchment scroll slipping out of the model and rolling under a piece of furniture. Meanwhile, detectives Thomson and Thompson are on the trail of a pickpocket, Aristides Silk. Tintin, later finds that the Unicorn has been stolen. He then visits Sakharine in Marlinspike Hall and accuses him of the theft when he sees a miniature model of the Unicorn, but when he notices that Sakharine's model is not broken, he realizes that there are two Unicorn models. Once Tintin returns home, Snowy shows him the scroll. Moments later, Barnaby arrives at Tintin's residence, but is fatally shot and killed. After reading an old message written on it, Tintin puts the scroll in his wallet, but it is stolen by Silk the next morning.
Le film devait initialement reprendre la trame des albums Les Sept Boules de Cristal - Le Temple du Soleil, avec une transition par Le Trésor de Rackham le Rouge pour l'introduction du professeur Tournesol qui ferait normalement son entrée dans la série, mais rien n'est actuellement confirmé.
Captain Haddock (Georges Wilson) learns that an old shipmate, Paparanic, has died and left him a ship, the Golden Fleece. Tintin (Jean-Pierre Talbot), Snowy and the Captain travel to Istanbul only to find that it is an old cargo ship in a really dilapidated state. While on board the ship the trio meet the ships cook Clodion and Paparanic's pet parrot Romulus. while outside the ship. A businessman named Anton Karabine (Demetrios Yra) claims to be an old friend of Paparanic and offers to buy the boat for "sentimental" reasons, but the huge amounts that he offers makes Tintin suspicious and on his advice Haddock turns the offer down.
Professor Calculus on (B&W) TV broadcasts an appeal to help end world hunger. He receives many letters and parcels and among them a blue orange which can grow in desert conditions (and glows in the dark) from Professor Zalamea, but no letter of explanation. That night, two thieves break into Marlinspike Hall and steal the blue orange. With no other choice, Calculus with Tintin, the Captain and Snowy go to Valencia (filmed in Burjassot, in Simat de la Valldigna at the Monastery of Santa María de la Valldigna, Gandia and Xàtiva).
Des explorateurs sont atteints d'un mal mystérieux après un voyage en Amérique du Sud. À Moulinsart, Bergamote, le dernier des explorateurs, tombe en léthargie après une coupure de courant et le professeur Tournesol est enlevé en bateau par de mystérieux individus. Tournesol a en effet commis un sacrilège en ayant porté le bracelet de la momie Rascar Capac, ramené par l’expédition.
Le film revient sur la carrière d'Hergé, mais surtout sur l'homme qu'il était, en mettant en image de nombreux extraits des bandes son originales des entretiens avec Numa Sadoul. La mise en scène, volontairement sobre, est accompagné de diverses images d'archives et d'entretiens avec des spécialistes et amis d'Hergé. Les divers entretiens avec des critiques suivent tous la même scénographie : ils se déplace dans une salle entièrement pavée de planches, s'arrêtent, les commentent, jusqu'à ce que la caméra aille se placer au-dessus d'eux, révélant les preneurs de sons, chef opérateurs, etc.
Tintin finds himself involved in a mystery of a drowned man, a regular tin of crab meat, and the name of a ship called the Karaboudjan. Upon investigating the ship, Tintin discovers that the shipment of tin cans contains not crab meat, but drugs. After learning about the ship's shady business, Tintin ends up becoming prisoner on the ship which already casted off from the port. The only way for Tintin to escape is by heading for dry land by life boat, and the only person to aid him is the ship's beer guzzling Captain named Haddock who is the only one on board not aware that his crew is trafficking drugs right under his nose.
One night, in Brussels, Belgium, a pair of crooks discreetly break into the aquarium and steal a priceless pearl. As soon as the security guards on duty see the empty shell, they rush away to raise the alarm. The crooks take advantage of the guards' absence by putting a fake pearl, the same size as the real one, in the shell. When the guards return with the director and the director sees the fake pearl, he thinks the guards were making it up, but then has second thoughts about the incident as a similar case happened at another museum two weeks before.