The movie starts with the purchase of a cheap model of a ship named the unicorn by Tintin and his dog snowy from in a marketplace. Evading offers for Ivan Ivanovich Sakharine and Barnaby who were desperately trying to buy the model, Tintin takes it home where it is broken during a chase of a neighbor’s cat by snowy. On breaking, a scroll falls out from within the ships mast which remains unseen by Tintin despite Snowy’s efforts to draw his attention to it.
Angry at snowy for breaking his model and somewhat perplexed by the behavior of the men who were so desperately trying to obtain the model, Tintin goes to the library where he finds out the mysterious past of the sunken ship which is said to carry tobacco and other hidden treasures.
on returning home from the library he finds his apartment in a mess and the broken model of the ship stolen and proceeds to meet the only person he could think of who stole it, Ivan Ivanovich Sakharine at his house, Marlinspike hall. He sees an identical model, but gets convinced it’s a different one and returns home. Barnaby is then shot while trying to warn Tintin about the dangers he was getting into and Tintin is shot at as well.
after a conversation with Thomson and Thompson, Tintin was returning home when he was abducted and kidnapped by Ivan Ivanovich Sakharine’s men and kept prisoner on board the SS Karaboudjan.
on regaining his consciousness he escapes to captain haddock who is perpetually drunk and together along with snowy they escape the ship on a lifeboat. Ivan Ivanovich Sakharine’s tries to relocate them are in vain as they capture the plane sent by him to find them and head towards the Bagghar port in morocco but crash in a desert on their way.
Due to a lack of alcohol, Captn. Haddock starts hallucinating about his ancestor who was the captain of the unicorn ship and during a fierce battle between him and a pirate named Red Rackham – Ivan Ivanovich Sakharine’s ancestor – loses, and chooses to sink the ship along with the treasures it held instead of letting it fall into the hands of the pirate. He tells Tintin this story along with the information of there being three models of the ship, each containing a scroll which when put together reveal the location of the sunken ship.
In Bagghar, they learn the second scroll is with a rich, wealthy man named Omar Ben Salaad who has incased it in a bullet-proof box. Ivan Ivanovich Sakharine plots to hold a concert with a famous singer whose powerful voice would crack the glass after which his trained hawk would swoop down and obtain the scroll. Possessing two scrolls, Ivan Ivanovich Sakharine proceeds back to Europe where he is ambushed by Thomson and Thompson whom he escapes from. This is followed by a battle between Sakharine and Captn. Haddock who like their ancestors engage in swordfight using dockside cranes, swords, and even bottles of whiskey. Haddock is eventually victorious and Sakharine is promptly arrested by Thomson and Thompson.
They then visit marlinspike hall, the indicated location and together find the third scroll down in the wine cellar behind a false wall. They also find some of the treasure, and putting the three scrolls together, the location of the sunken ship with the remaining treasures. They agree to go on their final adventure to find the sunken ship and with this, the movie comes to an end.
(Reference source : Ishaan Mehra.)