On board a train, Tintin reads the newspaper about seven explorers who have returned from a two-year expedition in the Andes, where they discovered the tomb of the Inca. The Captain, now a member of the group, invites Tintin to an evening at the music hall. There they witness a performance of a clairvoyant, Madame Yamilah who predicts the illness of one of the members of the expedition. They also view the act of Bianca Castafiore, as well as a knife thrower—whom Tintin recognizes, is General Alcazar former President. They have a glass of aguardiente with the general who introduces them to his assistant Chiquito.A mysterious illness begins afflicting the members of the expedition; one by one, they fall into a mysterious coma. The only clue is fragments of a shattered crystal ball found near each victim. Concerned, Tintin, Captain Haddock, and Professor Calculus go to stay with Calculus's old friend and only expedition member yet to be affected, the ebullient Professor Hercules Tarragon. Tarragon is keeping Rascar Capac's mummy in his house and is being tightly guarded against any attack. A lightning storm strikes the house and sends a ball of fire down the chimney and onto the mummy—which evaporates. Tarragon, clearly shaken, informs them a prophecy has come true:
A crystal ball
Rascar Capac has returned to his element and punishment will descend upon the desecrators.After Tintin, Captain Haddock, and Professor Calculus are each visited in their nightmares by the mummy, the three awaken to find Professor Tarragon comatose with the telltale shards of crystal by his bed. The attacker bypassed the police watch by coming down the chimney. The police shoot the attacker as he flees, but fail to capture him. Tintin states the crystal balls have done their work and claimed the last of the seven.Tarragon awakens and screams about mysterious figures attacking him, before slipping back into a coma. The plot thickens even further when Calculus takes a stroll around Professor Tarragon's house, discovers a striking gold bracelet, puts it on (remarking on how nicely it goes with his coat), and then mysteriously disappears. The bracelet had previously been worn by the now-vanished mummy.While searching the grounds, Tintin and Haddock discover the attacker had eluded them by taking refuge in a tree and deduce that he then jumped Calculus and stole the mummy's jewels. Tintin and the Captain are then fired upon by an unseen gunman who escapes, having kidnapped Calculus, in a black car. The alarm is raised and the police set up road blocks, but the kidnappers switch cars and slip through the net. Tintin visits a hospital where all seven of the stricken explorers go through the same horror—they awaken from their coma, scream about figures attacking
The hospital where all the members of the expedition were admitted
them, and slip back into their coma—at a precise time of day.Back at Marlinspike Hall, Captain Haddock is devastated by the loss of Professor Calculus. But after he receives a telephone call from the police, he disappears into his bedroom, then reappears—dressed as a sailor again and ready for travel. As he and Tintin drive to Westermouth, he explains the kidnapper's car was seen there; he believes the kidnappers boarded a ship with Calculus and he intends to follow. When they reach the docks, they find the kidnapper's car abandoned and they spot General Alcazar boarding a ship to South America. The General informs them his music hall career is over since the disappearance of his partner, Chiquito, one of the last descendants of the Incas. Tintin realizes Chiquito disappeared the same night Professor Tarragon was attacked and Calculus kidnapped he could be one of the kidnappers. Out of leads, Tintin and Haddock decide to go to a different dock, Bridgeport, to visit Haddock's friend, Captain Chester. Snowy retrieves an old hat found there, and Tintin recognizes it as belonging to Professor Calculus. Checking with the harbormaster, they discover that Calculus must be on board a ship, which is bound for Peru. They board a flight and resolve to meet his ship there.