Plot

The only way to save those who have been injected with the madness poison is by finding a doctor who can provide an antidote to cure them. However the doctor was kidnapped by the syndicate and is now being held hostage in Hukow outside the border of Shanghai. To make matters more difficult, Mitsuhirato has ordered the Japanese army station at the border of Shanghai to arrest Tintin if seen trying to exit the border of Shanghai. Tintin, will have to try to escape from Shanghai and head for Hukow to save the doctor and put an end to the syndicate once and for all. As well as learning who the mysterious leader of the organization is.—J LeGault

Tintin wants to help the Wang family by curing the insanity of their son. Wang says that only Professor Fang in Shanghai is capable for developing an antidote and it is too dangerous for them to travel to Shanghai.

Having obtained the real poison of madness with the help of the Wang's associate (who pretended to work for Mitsuhirato), Tintin returns to Shanghai, which has now been occupied by the Japanese Army, and tries to make contact with Doctor Fang Hsi-Ying, an expert on insanity, who may be able to cure Wang's son. Tintin enters the city disguised as a Japanese General, coming for inspection. But later, the General is found outside of Shanghai with his clothes stolen. Now, the entire Japanese army is looking for Tintin.

Tintin learns that Dr Fang had gone to meet Rastapopoulos at the Palace Hotel. As Tintin decides to meet Rastapopoulo, he finds a note at Dr Fang's door. Doctor Fang has been kidnapped by the drug cartel, presumably to prevent him developing an antidote to the poison. A note left by the kidnappers demands $50,000 in ransom money which must be paid at an old temple in the city of Hukow.

After a brief period of imprisonment in Shanghai by the Japanese Army, Tintin escapes and rides a train to Hukow to visit the temple where the ransom is to be paid, but a flood washes the tracks, and all the passengers must disembark. He rescues a young boy, Chang Chong-Chen, from drowning in the Yangtze River. They become fast friends, and Chang rescues Tintin from the Thompsons who had reluctantly arrested him under orders from Dawson (who is collaborating with Mitsuhirato to capture Tintin). But Chang steals Tintin's warrant and replaces it with a document stating that the Thompsons are escaped mental patients. The local police release Tintin and throw the Thompsons out. Tintin and Chang later travel to the area where the ransom money is to be left and are able to confirm that Doctor Fang has been kidnapped on Mitsuhirato's orders. At the Hukow temple Tintin is attacked by a Japanese assassin masquerading as a tourist photographer. Only quick action by Chang saves him.

Tintin and Chang return to Shanghai, but not before Wang and his family are kidnapped by Mitsuhirato. Tintin hides at the Blue Lotus to overhear that Mitsuhirato is expecting an Opium shipment at the docks that night. To find them, Tintin travels to the Shanghai docks and hides in one of the barrels being unloaded from an opium ship. But it turns out that he was seen, and when he emerges, he is confronted by Mitsuhirato armed with a gun, and soon finds himself a prisoner alongside Wang and his family. Then the boss of the opium cartel is revealed to be the film producer Rastapopoulos (see Cigars of the Pharaoh for back story). Tintin is appalled that a man he had thought to be a friend could be the gang leader until Rastapopoulos reveals the tattoo of Kih-Oskh on his forearm.

Fortunately, before the cartel could kill Tintin and Wang, the Sons of the Dragon, who had previously overpowered Mitsuhirato's thugs and had hidden in the other barrels (as planned by Tintin), reveal themselves, and force Mitsuhirato and Rastapopoulos to surrender. With Rastapopoulos arrested, the cartel is finally brought down, and Mitsuhirato commits suicide.

Fang Hsi-Ying finds an antidote to the poison of madness and Wang's son is cured (it is not mentioned whether the other victims of the poison are also cured). The ensuing political fallout over Tintin's involvement with the cartel and Japanese espionage leads to Japan's withdrawal from the League of Nations. The story ends with Chang being adopted by the Wang family and Tintin heading back for Europe.