The film is set in Turkey and Greece with the main characters of Tintin, Captain Haddock and Professor Calculus searching for a treasure after inheriting a ship called the Golden Fleece.

One of the clauses of Paparanic's will was that on accepting the ship, they also fulfill its current obligations, so after hiring 3 crewmen – Angorapoulos, Attila and Yefima, they set off for Athens to deliver the cargo.

Caught holding the gun, Tintin and Haddock are arrested but released thanks to the arrival of the policemen Thomson and Thompson, and on Papos' word, who is alive and recovering in hospital.

Tintin finds an old newspaper article showing that in their youth, Paparanic, Papos, Karabine, plus two strangers, were adventurers who were involved in a coup in the Latin American republic of Tetaragua, and formed a short-lived government.

He suffers from "memory loss", but for 1000 drachmas reveals that a large amount of gold is involved, and suggests that Tintin and Haddock consult the fifth man in the photo, Alexandre (Charles Vanel) who now lives in San Stefano monastery in Meteora.

Before departing, Father Alexandre gives Tintin and Haddock a bottle of wine which Paparanic gave him while visiting him last Christmas, and told him to drink only after his death.

Secretly, Yefima drains the fuel to prevent the ship from leaving port, but Tintin discovers him and throws him overboard in another bout of judo.

Fortunately, Calculus has invented a special tablet called "Super-Cuthbertoleum" which, mixed with the remaining fuel, is more than enough to enable the ship to reach their destination, the island of Thassika.

No sooner have the members of the Golden Fleece got the chest out of the water than they are held at gunpoint by Karabine, Angorapoulos, Yefima and their men who'd snuck aboard.

As the film ends, the local band helps Tintin, Snowy, Haddock, Nestor, and Clodion (their new cook) celebrate, while Calculus displays his latest invention: a flying birdcage for the parrot Romulus.

Marcel Bozzuffi, who plays the thug Angorapoulos, is best known as the hitman pursued in the famous car chase and shot by Gene Hackman in The French Connection.