The book begins with Asterix and Obelix hunting wild boar until one boar leads them to a Roman patrol, which the Gauls vanquish while the boars escape. In Rome, Julius Caesar orders M. Devius Surreptitious, the head of M.I.VI, service, to send an agent to infiltrate the Gauls. This agent is a Gaulish-Roman druid known as Dubbelosix, who travels in a folding chariot full of secret devices. Dubbelosix and Surreptitius communicate via a carrier fly, who develops a crush for Dubbelosix. In the Gaulish village, Getafix is depressed because he has run out of rock oil, which he requires to make the magic potion enabling the Gaulish resistance to Rome. The following day, Getafix is cheered by the arrival of Ekonomikrisis the Phoenician merchant but suffers a stroke upon hearing that he forgot to bring rock oil. When Chief Vitalstatistix tells Asterix and Obelix to fetch another druid to treat him, they discover Dubbelosix, who successfully revives Getafix with an alcoholic tonic. Asterix determines to go with Obelix and Dogmatix to obtain rock oil from Mesopotamia; Dubbelosix insists on coming, and they set off on Ekonomikrisis' ship. Along the way, they defeat pirates and Roman warships, while Dubbelosix secretly corresponds with the Romans, to arrange a blockade. The Phoenician ship finally lands at Judea, where Asterix, Obelix, Dogmatix, and Dubbelosix disembark for Jerusalem, where some sympathetic traders help the Gauls to enter secretly, in spite of an attempt by Dubbelosix to alert the city guards. Leaving him behind, Asterix and Obelix make contact with Ekonomikrisis' supplier, Samson Alius, who directs them to Babylon as the Romans have destroyed rock oil supplies in Jerusalem. In the Syrian desert, Asterix, Obelix, and Dogmatix find themselves caught up in ongoing wars between the Sumerians, Akkadians, Hittites, Assyrians, and Medes, much to Asterix's frustration. In the ensuing arrow battles, their waterskin is pierced, but they find a source of rock oil in the ground and carry some back to Jerusalem in the repaired waterskin. There, the two Gauls capture Caesar's personal ship, as well as Surreptitious and Dubbelosix. Near the coast of Gaul, Dubbelosix seizes the waterskin of rock oil and, as he tries to force it open, Obelix leaps upon him, spilling the oil into the sea. Asterix has lost all hope, but when they come back to the village, they find the Gauls fighting Romans as merrily as ever, and learn Getafix has replaced the rock oil in his potion with beetroot juice. Out of dismay, Asterix has a stroke, but after being cured with the new potion, convinces Getafix to perform experiments before testing him. Thereafter, the Gauls send Dubbelosix and Surreptitius to Caesar in a gift-wrapped box. Caesar sends them to the Circus Maximus as punishment for failure, where they are covered in honey and chased by bees, with the lovesick carrier fly following behind.
