The thirteenth ''Asterix'' book opens with a visit to the village by Chief Whosemoralsarelastix, a known Roman collaborator. Saying that Caesar is planning to raise taxes to fund new wars, he brought his village's treasury to the sole unconquered village in Gaul in a cauldron (that had recently held onion soup, giving the coins a distinctive odor) for safekeeping. After entrusting the cauldron to Asterix, the village holds a feast for the visiting chief and sends him on his way.

The next day, Asterix finds that someone had tunneled into his home and stolen all the sestertii from the cauldron. As punishment for failing in his duties, Vitalstatistix tells him that he must go into exile until he has either reclaimed or replaced all the silver that had been stolen from him. Asterix leaves the village, with Obelix volunteering to help him in his quest.

The two first check the local Roman camp of Compendium, only to find they don't have the money (and accidentally start a mutiny when the legionaries assume they now have to pay to be in the Legion rather than ''being'' paid). They run into the pirates (who, after being run aground by the Gauls during a previous encounter, have decided to convert their ship into a restaurant), but after beating them up, they learn that they don't have the money either (and persuade them to get out of the restaurant business and go back to sea). Heading to the nearest city, Condatum (called Rennes today), they try commerce (selling wild boars), and manage to crash the market value of pork by their poor understanding of economics. They try gladiatorial combat, only to find that the magic potion makes their victories so easy that they put the arena owner out of business. They try working in the theater, only to get their entire troupe arrested when Obelix shouts "These Romans are crazy!" in the presence of a high ranking official. They try gambling, and just lose money. They even resort to robbing a bank, only to find the bank empty due to Caesar's new taxes.

Finally, Asterix admits defeat, and decides that he must return the empty cauldron to Whosemoralsarelastix and then spend the rest of his life in exile to atone for his failure. But as he (and Obelix, who refuses to let Asterix go into exile alone) head to the chief's village, they encounter a Roman tax collector. After robbing the tax collector of enough silver to refill the cauldron, they resume their journey in much higher spirits - until Asterix realizes that the sestertii he put in the cauldron smell like onions.

Reaching Whosemoralsarelastix's cliff-top village, Asterix confronts the chieftain, saying the only plausible explanation for the coins stolen from the cauldron and the coins stolen from the tax collector both smelling like onion soup is if they were the same batch of coins. Whosemoralsarelastix was the man who stole the sestertii from Asterix's home, so that he could pay his taxes and remain in favor with the Romans, knowing that Asterix's village would do everything in their power to replace the 'stolen' money to redeem their honor after losing it, effectively making Asterix's village pay Whosemoralsarelastix's taxes for him. Realizing that he's been caught out, Whosemoralsarelastix orders his men to attack. While Obelix (who didn't understand Asterix's explanation at all) fends off the other Gauls, Asterix duels the chief. Asterix (who used up the last of his magic potion while robbing the tax collector) loses the duel, but before the chief can kill him, the cliff face crumbles, dropping the cauldron and the silver it held into the sea (or rather, onto the head of a certain pirate captain who coincidentally was sailing past at that moment, but the Gauls don't know that).

As Whosemoralsarelastix mourns the loss of his money, Asterix and Obelix return home with their honor restored, and are welcomed home by a feast.
* AllPartOfTheShow: The Legionaries storming Laurensolivius' play are believed to be this by the audience.
* BrokeEpisode: Variant, as Asterix and Obelix try to recover coins in a Gaul broken by Caesar's military expenditures.
* BulkBuyOnly: Due to his lack of greed (and complete ignorance of economics), Asterix ends selling fourteen wild boar for five coins. And as a BrickJoke, it causes a price fall revealed by a restaurant owner.
* ChekhovsGun: When Whosemoralsarelastix tells the village what he would like them to do, he mentions that the cauldron he brought full of money previously contained onion soup. When Asterix and Obelix get the money from the tax collector at the end, Asterix notices that it smells like onions...
* ComicallyMissingThePoint:
** Obelix is also unable to get his head around the idea of throwing onion soup ''away'' from a cauldron to put money instead.
** Asterix and Obelix are in a restaurant. The waiter brings them two boars, and Asterix asks him what the building over the road is. The waiter explains that it's a bank, where the Romans keep their money. After he goes:
--->'''Asterix''': You know what we're going to do?\\
'''Obelix''': Eat our boars?
** When Obelix is casing the bank, the guard on duty accuses him of being a potential bank robber, and boasts of the bank's security while [[IllNeverTellYouWhatImTellingYou also telling him when the guard changes and where the catch for the vault is hidden]]. Obelix returns to the inn where he and Asterix are staying and reports... that the guard saw straight through him before he could get any information.
* CreatorCameo: Goscinny and Uderzo appear in the audience at the theatre. Uderzo is telling the prefect he thinks the performance should be good, while Goscinny is on the right-hand side of the picture, doing what he did best in reality: making those around him laugh.
* DoingItForTheArt: InUniverse example. The actors refuse the offer of a breakout because their execution gives them an opportunity to perform in the Colosseum.
* HollywoodDensity: A metal cauldron filled to the brim with silver coins would be rather heavy, but Asterix can carry it without using the magic potion, and Redbeard manages to survive the cauldron falling on his head from the top of a cliff without serious injury.
* IllNeverTellYouWhatImTellingYou: A guard tries to dissuade Obelix from robbing the bank by explaining every single detail of its security. Too bad Obelix wasn't paying attention.
* ITakeOffenseToThatLastOne: Laurensolivius' play is built to [[TakeThatAudience shock and offend]]. The prefect gets way too offended once a stage frightened Obelix murmurs "These Romans are crazy", and he orders an arrest of the actors. [[AllPartOfTheShow Which the audience mistakes for part of the play.]]
* NamedAfterSomebodyFamous: The actor who eventually hires Obelix to his play, [[Creator/LaurenceOlivier Laurensolivius]] ([[ Eleonaradus]] in the original French).
* NoodleIncident: Nobody says exactly what happened to the one tax collector who tried collecting taxes from Asterix's village, but whatever it was they did, nobody ever tried to do that again.
-->'''Vitalstatistix:''' What ''fun'' we had! Remember when...?
-->'''Getafix''' ''(drowns out the rest with hysterical laughter)''
* NotSoInnocentWhistle: Obelix starts whistling innocently as they break into the bank... and doesn't stop until after Asterix sees the place is empty.
* SpeechBubbles: The tax collector speaks entirely in forms.
-->'''Tax Collector:''' Are you:
--->'''A:''' Ordinary passersby?
--->'''B:''' Motivated by friendly intentions?
--->'''C:''' Bandits?
-->'''Asterix:''' Give us your money if you don't want to get thumped!
-->'''Tax Collector:''' Are you:
--->'''A:''' Ordinary passersby?
--->'''B:''' Motivated by friendly intentions?
--->'''C:''' ''(checked)'' Bandits?
* TakeThat: The tax collector is a caricature of future French President Valéry Giscard d'Estaing. When the book was written in 1968, Giscard d'Estaing was between his two tenures as Minister of Finance.
* ThrowTheDogABone: And for once, just for once, the pirates are happy!
* TrueCompanions: The order of banishment applied to Asterix alone. Obelix goes with him purely out of loyalty to his friend.
* WhoWouldWantToWatchUs: Obelix suggests that he and Asterix raise money by telling stories about their adventures ("We could call them ''The Adventures of Obelix the Gaul''..."). Asterix disapproves.