While browsing in an outdoor market with his pet dog Snowy, Tintin, a young journalist, purchases a miniature model of a ship known as the "Unicorn", but is accosted by two men, who both separately unsuccessfully attempt to acquire the model from Tintin. After Tintin takes the model home to his apartment, it is accidentally broken during a chase between Snowy and a stray cat; a metal tube slips out of the ship's mast and rolls under Tintin's furniture. Meanwhile, bumbling police detectives Thomson and Thompson are on the trail of pickpocket Aristides Silk, whom Snowy had seen in the market.