As the book begins, Asterix and Obelix are in Rome, where a thoroughly fed up Asterix is venting his frustration on Obelix for landing them in their predicament. The story pauses and rewinds to explain what Asterix and Obelix are doing in Rome to begin with
An unwilling Asterix and Obelix have accompanied an even more unwilling Vitalstatistix on a visit to Lutetia with his wife, Impedimenta, to see her wealthy and uppity brother, Homeopathix, who has always looked down on Vitalstatistix. Over the course of the evening, Vitalstatistix gets very drunk and, tiring of Homeopathix' snobbery, bets him that he can cook him a stew flavoured with Julius Caesar's laurel wreath. The equally drunk Obelix declares that he and Asterix will go to Rome on the chief's behalf to get the wreath, and Vitalstatistix angrily rebuffs Asterix' attempt to talk his way out of the quest.
Flash back to the present; Asterix points out to Obelix that their usual tactic of marching in and beating up every Roman they see will not work with the crack troops guarding Caesar's palace. They notice a man leaving the palace; plying him with drink, they learn he is a slave, purchased from Typhus, Caesar's personal supplier. They decide to offer themselves as merchandise to Typhus, but when the other slaves on Typhus' stand dismiss them as cut rate junk, a fight breaks out, with Asterix and Obelix triumphant. An amused patrician offers to buy the two Gauls, who assume he is Caesar's major-domo (whom Typhus has been expecting at any minute) and that they are finally on their way to Caesar's palace.
However, the patrician, Osseus Humerus, has actually bought the Gauls as slaves for his own household, which includes his wife Fibula, his daughter Tibia, and his alcoholic son Gracchus Metatarsus; they quickly earn the enmity of Humerus' own major-domo, Goldendelicius, who is determined not to let these fragile Typhus trinkets replace him. Asterix and Obelix, however, are more interested in getting Humerus to return them to Typhus to be bought by Caesar, and try everything they can to get the sack. They throw everything in the kitchen into a disgusting stew, but this only succeeds in curing Metatarsus' hangover. They march through the house in the middle of the night banging pots and pans, but they only inspire the family to have a loud, drunken party.
Fortunately for the Gauls, Humerus has business at Caesar's palace the next day; as he is too hung over from the previous night's party to go himself, he sends the delighted Gauls in his place. However, Goldendelicius, ever more paranoid about being replaced as major-domo by Typhus' museum pieces, has gone ahead of them and reported them as assassins plotting to murder Caesar, and they are arrested and imprisoned. Still, they're in the palace at last, and that night, they search the palace in secret, knocking out every guard they pass as quietly as possible. The search turns up empty, and Asterix vows to continue the next night.
The next day, the scene of disarray prompts the panicked Romans to schedule the two Gauls' trial for that very day, and the lawyer Nisiprius arrives to defend Asterix and Obelix. He notes their conviction is assured, and Asterix is intrigued to learn that this will mean being thrown to the lions in front of Caesar himself. As the trial's verdict is already known, Nisiprius plans to use it as a chance to show off his oratory skills, but when the prosecutor begins to give the same speech, Nisiprius tries to have the trial postponed. The impatient Asterix interrupts and makes an impassioned plea to the court that their crimes - wrecking Typhus' stand, getting into Humerus' house under false pretences to get closer to Caesar to assassinate him - cannot be overlooked, and the emotionally overwhelmed court sentences them to be thrown to the lions.
However, on the day their sentence is to be carried out, the jailer reveals that Caesar is away fighting the pirates, and Asterix and Obelix refuse to go into the arena. The animals end up devouring each other, and the enraged crowd starts a riot, during which the Gauls escape.
Sleeping rough on the streets of Rome, they are nearly attacked by a group of thieves; impressed by Obelix' strength in rebuffing their attempted theft, they decide to recruit the two Gauls into their gang, and the next night they are ordered to rob a young drunk. The drunk turns out to be Humerus' son Metatarsus, who is ecstatic to see them again. After thrashing the bandits to save Metatarsus from harm, Asterix and Obelix learn that he has been celebrating with Goldendelicius, who was made Caesar's personal slave after denouncing the Gauls as assassins, and will be holding Caesar's laurel wreath over his head during his triumphal procession after his victory over the pirates.
Metatarsus directs the Gauls to Goldendelicius in exchange for the recipe for their accidental hangover cure. Asterix and Obelix corner the still drunk Goldendelicius and force him to give them the laurel wreath in exchange for a parsley wreath. No-one notices the difference during the triumph... except perhaps for Caesar himself, who feels strangely like a piece of fish.
Back in the village, Homeopathix is finally sitting down to the stew flavoured with Caesar's laurels as Vitalstatistix enjoys his victory. However, the unimpressed Homeopathix begins criticising the cut of meat used in the stew, and the chief's anger finally boils over as he punches his brother-in-law sky high. The dazed Homeopathix lands in front of the bound Cacofonix, who wonders if Homeopathix was also punished for trying to sing, while the concluding narration notes that the Gauls' hangover cure led to a surge in drinking among the Romans, and ended up causing the decline and fall of the Roman Empire.
- Character Focus: Even by the usual standards of the "Asterix and Obelix go on a journey" albums, this album keeps the main duo front and centre from start to finish. The only other series regular to even get a look in outside the final panel (never mind the final page) is Vitalstatistix, who only appears in the Lutetia flashback and the final banquet. Even Dogmatix is almost completely absent.
- Continuity Nod: As in Asterix and the Cauldron, Asterix and Obelix demonstrate a complete lack of understanding of economics. When Humerus offers to buy them from Typhus, he asks Asterix to name his price; he suggests five sestertii. The British slave on Typhus' stand intervenes, saying the sale will crash the slave market, and suggests a more suitable price of... ten sestertii. (The almost apoplectic Typhus, meanwhile, cannot get a word in edgewise.)
- Elite Mooks: The legionaries guarding Caesar's palace, according to Asterix, one reason he tells Obelix they cannot simply march into the palace, bash every Roman they see, grab the laurel wreath, and leave again. However, at night, fought one at a time, the palace guards prove no match for Obelix.
- Fed to the Beast: Asterix and Obelix get themselves sentenced to be thrown to the lions in the hope of getting Caesar's laurel wreath directly from the great man's head. Obelix has an attack of stage fright the night before their "appearance", and asks the jailer if he can have some of the oil the gladiators wear to smarten himself up a bit. The jailer suggests mustard might be more appropriate.
- Foreign Queasine: Continuing the series' tendency to mock British cooking, Humerus says the Gauls' cooking could hardly be any worse than that of their previous cook, the Briton Autodidax. Of course, when Asterix and Obelix simply throw everything in the entire kitchen into a single cauldron (including soap), they decide that perhaps Gaulish cooking isn't what its reputation usually suggests...
- Getting Crap Past the Radar:
- This exchange between Vitalstatistix and his brother-in-law:
: But my dear chap, where am I going to put all these menhirs of yours? Vitalstatistix (with an evil grin)
: You really want me to tell you? Impedimeta
- The panoramic scene of the slave market features a topless female slave on one of the stands in the background.
- Hideous Hangover Cure: While trying to get thrown out of the Roman family they've become slaves to, Asterix and Obelix wind up creating one. The narration states that this allowed Romans to drink without consequence, leading to the decline of Rome.
- In Medias Res: The story starts with our heroes already in Rome before explaining how they got there; the panels actually "stop and rewind" to tell us how the story really began.
- Made a Slave: Inverted, they're trying to become slaves in Caesar's palace, so as to get access to Caesar's laurels.
- Obnoxious In-Laws: Homeopathix, the wealthier brother of Impedimenta, barely even makes the effort to remember Vitalstatistix' name. In the final banquet, when Vitalstatistix makes good on his promise to cook a stew with Caesar's laurels, Homeopathix, far from being impressed, criticises the meat for not being a choice cut or well cooked.
- Running Gag:
- In the original French, the drunken Obelix and Vitalstatistix make the verbal slip of saying "Farpaitement" instead of "Parfaitement" ("Perfectly") during the dinner with Homeopathix; the word recurs throughout the rest of the book when either Obelix is drunk or Asterix is feeling especially bitter. In English, the word is translated as one of two internal spoonerisms, depending on context: "Zigackly" (for "Exactly") and "Ferpectly true" (for "Perfectly true").
- Asterix and Obelix seem to be completely unable to get a good night's sleep while in Rome, to Obelix' ever-increasing anger. On their first night as Humerus' slaves, they are kept awake by the family having a loud party (though they only had themselves to blame for this); when imprisoned in Caesar's palace, they are woken by the guards barging into their cell (and as they have spent the night searching the palace, they have had hardly any sleep); when sleeping in a doorway in Rome, they are almost robbed by bandits.
- The vain, muscular Greek slave on Typhus' stand whom Asterix eventually punches outnote adopts the poses of a variety of classical statues, including Rodin's The Thinker, the Apollon of Olympia, Laocoon and His Sons (in the course of imitating which he entangles Asterix in a rope), and the Diskobolus of Myron.
- The animal keeper in the arena who has had to watch the animals eat each other as Asterix and Obelix refuse to go into the arena is a caricature of French actor and circus owner Jean Richard (whose other claims to fame include a 23-year stint on French television as Jules Maigret).
- Caesar's campaign against the pirates may be a reference to an incident in the life of the real Gaius Julius Caesar in which he was kidnapped by pirates and held for ransom (the amount of which they increased at Caesar's own suggestion). After the ransom was paid, Caesar told the pirates he would return to kill them one day; the pirates assumed he was joking. He wasn't.
- Spit Take: Astérix spits out his food when chief Vitalstatitix announces that they're going to cook a stew with Caesar's laurel wreath as ingredient.
- Springtime for Hitler: After becoming slaves, Asterix and Obelix find out that the Roman family that bought them aren't close to Caesar, and do everything they can to be abandoned, only for their antics to please the family instead.
- Stiff Upper Lip: One of the slaves on Typhus' stand (and the only one to be friendly toward Asterix and Obelix) is a Briton, who has the usual stoic expression seen on Britons in the Asterix series, and seems completely unruffled by the fight that leaves Typhus' other slaves bruised and unconscious.
- Theme Naming: In the English version, Humerus and his wife and children are all named for bones in the human skeleton; even Humerus' first name, Osseus, is a pun on "osseous", meaning "turned into bone".