Dupond et Dupont
While on Müller's trail, Tintin meets his old friend, the Portuguese merchant Oliveira da Figueira. With Figueira's help, Tintin enters Müller's house and knocks him unconscious. He finds the prince imprisoned in a dungeon and rescues him as Haddock arrives with the authorities. Müller is revealed to be the agent of a foreign power responsible for the tampering of the fuel supplies, having invented a type of chemical in tablet form, codenamed Formula 14, which increases the explosive power of oil by a significant amount. Thomson and Thompson find the tablets and, mistaking them for aspirin due to their being packaged as such, swallow them, resulting in them growing long hair and beards that change colour. After analysing the tablets, Professor Calculus develops an antidote for Thomson and Thompson and a means of countering the affected oil supplies.