Hergé concieved the idea with Greg in 1958. Staff at Hergé Studios were mixed. Half liked the thought of another action story, while the other half saw it as just a rehash of the The Calculus Affair. After making 8 pages of sketches, Hergé agreed with the second half and abandoned the project.
Hergé still thought the idea had merit and planned to make Tintin and the Thermozéro the plot of a third animated film, but once again, this did not take place. Hergé then asked his assistant Bob de Moor to change the plot slightly and make it the sixth Jo, Zette and Jocko adventure though it likewise fell through.
One rainy day, Tintin, Captain Haddock and Professor Calculus survive a car crash with a German man they had just previously met a few minutes earlier. Tintin drags him out of the car and covers him with his coat. Interestingly, multiple people attempt to take custody of the man in their cars before the ambulance arrives. The man secretly hides an object in Tintin's coat without anyone noticing. After the ambulance arrives to take the man, everyone retires.
Back at their hotel, the Professor decides to take Tintin's coat to the laundry. A few days afterwards, Tintin and Captain Haddock discover that everyone who was present at the accident had been burgled. Apparently, the culprits were looking for an item that belonged to the victim, the one he put in Tintin's pocket. The next day, Captain Haddock is kidnapped and a message for the ransom reads: "Haddock for the item."
A meeting is convened in Berlin. Although still unaware of what the item is, Tintin, Snowy and Calculus travel to Germany to get Haddock back. With a briefcase in his hand, Tintin meets the kidnappers face to face. A few minutes later they are all captured and imprisoned, as Tintin's case carried a transmitter. Back in Marlinspike, Calculus discovers that the item is an explosive that functions in spaces without any oxygen. He also learns that it cannot work as one component is still absent.