After the Siege of Alesia, Gaulish chieftain Vercingetorix throws his arms down at (or rather, ''on'') Caesar's feet, and Gaul is officially conquered. Caesar (hopping on one foot) sets off in search of other conquests, and the arms are lie where they have fallen. A Roman archer succumbs to temptation and steals the shield, and loses it in a game of chance to another legionary. That legionary is caught sneaking around at night without a pass by a centurion, who takes the shield in exchange for his silence. The centurion swaps the shield for an amphora of wine at a wine and coal merchant's, and the merchant gives the shield to a Gaul who survived Alesia...
...Jump to the present, where Chief Vitalstatistix is suffering. Too much wine and fine food is giving him liver trouble. Getafix prescribes treatment from a Hydro (health spa) in Aqua Calidae (present day Vichy). With Asterix, Obelix, and Dogmatix accompanying, the Chief leaves, sampling fine food from various inns along the way and making his liver trouble worse. At the Hydro, Vitalstatistix begins his treatment, and Asterix and Obelix, after causing a bit of trouble with their merry-making, are firmly asked to leave, with their chief promising to meet up with them in Gergovia.
After leaving, the Gauls bump into Roman tribune Noxius Vapus, and thump him accordingly. Afterwards, they meet wine and coal merchant Winesanspirix, who offers to show them around Gergovia. In Rome, Vapus reports his thumping to GaiusJuliusCaesar, who decides to put the Gauls in their place by holding a triumph on the Chieftain's Shield - but the shield is missing. Caesar puts Vapus on the trail, telling him to start his search in Gergovia, where many survivors from Alesia settled in.
Vapus enlists the local legions, and one legionary, the incredibly lazy Caius Pusillanimus, is selected to go undercover, as he's so foolish that no one will take him for a spy. Unfortunately, he lets slip what's going on to Asterix and Obelix, and they resolve to find the shield first. Both sides follow the trail from Circumbendibus (the archer who first picked up the shield), who now owns a wheel-factory in Nemessos (Clermont-Ferrand today), to Marcus Carniverus (the legionary who won the shield in a game of chance), now owner of his own inn, to the alcoholic Centurion Titus Crapulus (the Centurion who confiscated the shield), who reveals the name of the wine-dealer he gave the shield to - Winesanspirix! Both sides race to the Gergovian's inn, and while the Romans fail to find Winesanspirix in the coal cellar, Asterix and Obelix catch up with him. Winesanspirix admits that after Alesia, he gave the shield to a sad and miserable little Gaul...
...and in walks Vitalstatistix, looking sad, miserable, and ''very'' little from his treatment. Winesanspirix recognizes him as the Gaul from Alesia, and asks if he still has the shield. Of course Vitalstatistix still has it, he never leaves home without it...it's the shield he's always being carried on!
Meanwhile, Vapus and his legionaries prepare to sack Gergovia when they meet up with Caesar, who wants to know how the search is going. At this point they witness the Gauls holding their own triumph with the shield, carrying Vitalstatistix. Knowing that he has to keep this humiliation secret, Caesar has Vapus and his troops sent to a garrison in Numidia, and has Crapulus and Pusillanimus made into commander of the Gergovia and Centurion respectively, on the grounds that they aren't filthy from searching coal cellars (they were too busy getting drunk). The two drunks promise to keep things quiet in Gergovia, as they're already friends with all of the wine sellers.
Our heroes return to their village in triumph, and along the way Vitalstatistix samples fine food from the various inns along the way, restoring his original bulk by the end of their journey. On his return, the village holds another one of their feasts, but someone is missing. Cacofonix? No, he's enjoying this one. The missing person is Vitalstatistix, who's being shown the offensive qualities of the shield from Impedimenta...
!!Tropes present in this story
* AgonyOfTheFeet: Let's just say that Vercingetorix was not a completely graceful loser.
* ArtEvolution: Albert Uderzo was experimenting with a new art style for this book, with less round character designs and less bright colours. He later admitted the experiment was not altogether successful in his eyes.
* BerserkButton: Don't mention Alesia to the Gauls.
* CherryTapping: Vitalstatistix is perfectly fine sampling the many (many) local foodstuffs on the way to the cure, until he lies down under a tree, a leaf falling off to land on his stomach... sending him in horrifying pain (he can't even stand the doctor ''looking'' at him).
* DietEpisode: Vitalstatistix is forced to go on a severe diet to cure his liver trouble; when he arrives in Gergovia near the end of the book, he has slimmed down almost to Asterix' size. (Since he was similarly thin when he was younger, Winesanspirix, who has not seen him since he gave him Vercingetorix' shield, recognises him immediately.)
* EveryEpisodeEnding: The usual ending is subverted in this case. Cacofonix is happily devouring a leg of boar at the banquet... whereas Vitalstatistix is being forcibly kept at home by his irate wife.
* FoodPorn: Both on the way to the spa and during, since Asterix and Obelix are under no obligation to follow the water and soup diet.
* InnocentlyInsensitive[=/=]SelectiveObliviousness: Asterix and Obelix fail to realize what poor manners it is to eat rich food around spa patients.
* InVinoVeritas: When Pusillanimus goes undercover to gather information about the whereabouts of Vercingetorix' shield, he immediately gets stinking drunk at Winesanspirix' inn, and reveals not only that the Romans are looking for the shield for a planned triumph for Caesar, but that he personally saw Lucius Circumbendibus make off with the shield after the Battle of Alesia, and that Circumbendibus now owns a wheel factory in Nemessos (facts he hasn't bothered to tell his superiors).
* LostInTranslation: In the original French, the Arvernians speak with an exaggerated version of the modern Auvergne accent, replacing all "s" sounds with "sh". This sets up many puns and references (for example, a young Arvernian who doesn't speak with the accent not because the Arvernian accent is fading among the young generation, but because "he lishpsh") which don't translate as well into other languages; in the English version, they were mostly replaced with meat-related puns.
** Mentioning Alesia (the place where Caesar annexed Gaul into the Roman Empire) will cause Gauls to angrily deny knowing where Alesia is. [[HistoricalInJoke The joke is that at the time of this story's printing, the location of Alesia really WAS unknown (and that the denial is how people lost track of it)]].
** People getting dirty from close contact with coal cellars. The fact that Pusillanimus alone is clean after the first inspection of Winesanspirix' coal cellar alerts his commander to the fact that he skived off actually searching it.
* SchmuckBait: Vitalstatistix leaves in a hurry when Impedimenta reacts badly to the suggestion that his departure should be accompanied by a banquet. Fulliautomatix, seeing the chief leave with Asterix, Obelix, and Dogmatix, is shocked that they're not telling anyone they're going, and bounds up the stairs to Cacofonix' house. He tells Cacofonix the chief is leaving... and, sure enough, the bard takes the bait and declares he will sing them a song of farewell, leading Fulliautomatix to start bashing him in while yelling, "OH NO YOU WON'T! OH NO YOU WON'T!"
* SpeechImpediment: Inverted in editions where the "'s' as 'sh'" facet of the Auvergne accent is preserved by the translation.[[note]] For example, it is preserved in the German translation, but not in the English one.[[/note]] Obelix initially thinks this is a speech impediment, and has to be tactfully dissuaded from drawing attention to it by Asterix. Only one Arvernian boy can pronounce the letter S as it is pronounced in the rest of Gaul, and according to his elders, this is because "he lishpsh."
* StatusQuoIsGod: Vitalstatistix regains all the weight he lost at the spa by the time he returns home.