The film's plot focuses on Asterix and Obelix transporting a barrel of Magic Potion to a rebel village of Britons, as they attempt to hold out against the Romans.

Sensing his chief does not have much hope of lasting much longer, Anticlimax decides to travel to Gaul and find his cousin Asterix, in order to secure some of the Magic potion that his village uses to hold back the Romans.

The druid Getafix obliges to the request to supply a barrel of potion to help, upon his arrival, with Vitalstatistix assigning Asterix and Obelix, accompanied by Dogmatix, to transport it to Britain.

Unknown to the group as they reach the British shoreline, Roman officer Stratocumulus, a passenger on the galley who was returning to Gaul, overhears Obelix unintentionally state their mission following the fight.

Using a pot of hot water, infused with the herbs, the Britons swiftly drink it and find the courage needed to defeat the Romans, much to the disappointment of Motus and Stratocumulus.