Tintin et le Thermozéro (1958)

On a rainy day, Haddock, Tintin and Calculus have a car accident with a German they previously had words a few minutes before. Tintin, ready to help people, draws him out of his car and covers him with his coat. Surprisingly, many people try to put the man in their own car before the ambulance arrives. He hides an object in Tintin's coat without anyone's knowledge. Finally, the ambulance arrives and everyone goes home.
Back at the hotel, Calculus decides to bring Tintin's coat to the laundry. A few days later, Tintin and the Captain discover that everyone present at the accident has been burgled. Apparently, the people behind all this are looking for an item that previously belonged to the victim. The next day, Haddock is kidnapped and the message for the ransom is "Haddock for the item". A meeting is set in Berlin. Though unaware of what the item is, the heroes travel to Germany to get Haddock back. With a case in his hand, Tintin meets the kidnappers. A few minutes later they are all jailed, as Tintin's case carried a transmitter. Back in Marlinspike, Calculus discovers the item cannot work as one ingredient is missing.