Goscinny and Uderzo were not satisfied with the film, and managed to block the release of the planned sequel, Asterix and the Golden Sickle (likewise made without their involvement).

Their state upon their return to camp prompts the leader Phonus Balonus to seek the secret behind the Gauls' superhuman strength.

Phonus selects a volunteer (by means of a single round of musical chairs) to pose as a Gaul in order to infiltrate the village; the unlucky loser is a short, slack-tongued misfit named Caligula Minus.

Minus is debriefed by Phonus Balonus, who on learning of the magic potion orders his legionaries to capture Getafix and bring him back to the camp.

After benefiting from Asterix's common sense the merchant agrees to take him to the Roman camp on his cart, hidden in a pile of hay until nightfall.

Believing that the potion Getafix has made is the same as that which gives the Gauls their strength, the Romans drink it and discover, much to their dismay, that it is in fact a hair-growing formula.

Just as the pair begin to overpower their captors, Phonus receives a surprise visit from Julius Caesar who – dismayed by the state in which he finds the camp – asks to meet the Gauls.