[[quoteright:300:http://static.tvtropes.org/pmwiki/pub/images/album-tintin-seven-crystal-balls_4866.jpg]]Tintin goes to visit Captain Haddock and Professor Calculus at their new home in Marlinspike Hall. On the train, he reads about a team of seven explorers led by Professor Sanders-Hardiman returning home after a two year expedition in the Andes where they discovered the tomb of the ancient Incan priest Rascar Capac, with the latter's mummy in tow. A strange man compares them to the Egyptologists who unearthed Tutankhamen's tomb and claims the same fate will befall them. Later on, Tintin attends a music hall with Haddock and is surprised to find General Alcazar, having been deposed of power and now performing as a knife thrower. Another act by a psychic also mentions the Incan expedition and claims its members are in grave danger.

Concurrent with these events, each member of the Sanders-Hardiman expedition starts falling into a mysterious coma, one by one. Thompson and Thomson are investigating and reveal that the only clue present at each scene are fragments of crystal spheres, which apparently contained some sort of mysterious gas that caused the comas. Despite the efforts of Tintin, Haddock, and the Thompsons, they are unable to stop the attacks and finally decide to personally guard the last explorer, Professor Tarragon, an old friend of Professor Calculus, who accompanies them to the former's house. After the Rascar Capac mummy disappears from the house in a mysterious bolt of ball lightning, Tarragon claims that this is the culmination of a prophecy: Rascar Capac has "returned to his element" and will go after Tarragon personally. Despite the escort, Tarragon succumbs to the coma as well, becoming the last of the seven. To make matters worse, Professor Calculus is kidnapped after finding the mummy's bracelet.

Tintin and Haddock chase the kidnapper and manage to track him to the ''Pachacamac'', a ship bound for Peru. Tintin also discovers that Alcazar's assistant Chiquito, one of the last descendants of the Incas is also involved. Tintin and Haddock depart for Peru to rescue Calculus, closing part 1 of the two part story that concludes in ''[[Recap/TintinPrisonersOfTheSun Prisoners of the Sun]]''.

!!Tropes
* AndIMustScream: The seven explorers themselves, especially Professor Tarragon.
* CallBack: See below.
* ContinuityLockout: An extremely minor example, but when our heroes are contacting the explorers to warn them of the curse, Professor Cantonneau greets Tintin as an old acquaintance ("My dear Tintin" in the English). This is because Cantonneau was also one of the experts aboard the Aurora in ''[[Recap/TintinTheShootingStar The Shooting Star]]''. It's a nice little grace note, but perhaps too subtle: in stark contrast to most of the series' numerous [[CallBack callbacks]], there isn't a word of explanation as to how the professor already knows Tintin. So, those happening to read ''Crystal'' before ''Star'' are liable to be puzzled (indeed, given Cantonneau's minimal role in ''Star'', even those reading in order may have forgotten about him). Of course, it wouldn't be too much to suppose that Tintin had already met Cantonneau in a non-adventuring context, but that would be surprisingly rare for this protagonist: unlike e.g. Haddock and Calculus, Tintin is shown to have virtually no ''a priori'' acquaintances (with the obvious exception of Snowy). For just about anyone he recognizes, you can find them meeting for the first time somewhere earlier in the series.
* {{Curse}}: The explorers and archaeologists all fall victim to a curse due to desecrating a tomb.
* DangerousWindows: Two of the members of the Sanders-Hardiman expedition fall victim to crystal balls hurled through their windows. Professor Cantonneau is attacked this way just as Tintin tries to warn him not to go near the window. Dr. Midge is then placed under police guard, but the police in question are Thompson and Thomson, and they try to guard everything but the window. With predictable results. [[CatchPhrase To be precise]], the two of them freak out over a brown paper package, fearing it contains a bomb or pathogen, and ''both'' go into another room to examine it, leaving the professor completely unguarded. [[RedHerring The package has a butterfly specimen in it.]]
* FaintingSeer: Mrs. Yamilah, a stage fortune teller, tries to look into the fate of a woman married to one of the explorers. She gets a glimpse into the fate of the husband and seems physically affected.
* {{Fireballs}}: A huge fireball of lightning crashes into the protagonists' household. What some readers may be amazed to know is that this phenomenon actually has some basis in reality. Ball lightning is one the least understood meteorological phenomena known to man. Essentially a ball of light that occurs during a thunder and or lightning storm, these little (or huge) buggers have been known about since antiquity. Nobody knows exactly what the stuff is though, other than a ball of light with electric properties. Its reported characteristics vary wildly, some times it can pass though people without out harming them or times they discharge massive amounts of electricity, even up to a normal lightning strike.
** ScienceMarchesOn: Up until the 1960's (the story was first serialized in the 1940's) scientists were skeptical of the very existence of ball lightning, putting them on the level of {{Flying Saucer}}s and other hocus pocus. Hence their mystical properties as shown on the book cover.
* HighClassGlass: In the previous adventure of the series, Captain Haddock had acquired a treasure through inheritance. His newfound wealth is indicated in this album by his residence in a mansion and by his new habit of wearing a monocle. Not being accustomed to them, he loses a lot of them.
* KnifeThrowingAct: General Alcazar, exiled in this book, has his own stage act. After creating a full KnifeOutline around his Indian target, he asks an audience member to blindfold him. His blind throw hits right in the center of the fruit held over the target's chest.
* AMythologyIsTrue: In-story example. The curse of Rascar Capac is scoffed at by the rational characters. Until it turns true to the letter.
* NightmareSequence: Tintin and his companions all have the same nightmare: that they are visited by the Inca mummy Rascar Capac who enters their bedroom by night and then throws a crystal ball on the floor.
* NoCommunitiesWereHarmed: The story accurately depicts the French port of Saint-Nazaire. The English translation renames it Westermouth for no good reason.
* RuleOfSeven: Seven cursed explorers, seven crystal balls hurled at them and and placing them in comas.