The Romans having been humiliated many times by the rebel Gauls, Felonius Caucus, advisor to Centurion Nebulus Nimbus, suggests a single combat between Vitalstatistix, chief of Asterix’s tribe, and the Gallo-Roman Chief, Cassius Ceramix of Linoleum. According to ancient Gaulish customs, the loser would forfeit his entire tribe to the winner. When Ceramix argues that Vitalstatistix would surely win with Getafix’s magic potion of invincibility, Caucus sends a patrol to capture Getafix before the challenge is confirmed. Whilst attempting to scatter the attackers, Obelix accidentally strikes Getafix with a menhir, the impact of which causes amnesia and insanity.
Following Cassius Ceramix’s challenge, Asterix and Vitalstatistix attempt to restore Getafix’s mind by experimenting in potions; but this produces only a whimsical sub-plot, in which the Roman soldier Infirmofpurpus, captured by Obelix as a test subject, is temporarily rendered weightless. Thereafter Asterix and Obelix consult Psychoanalytix (original French name is Amnesix), a druid who specializes in mental disorders; but when asked to demonstrate what caused the problem, Obelix crushes Psychoanalytix with a menhir, leaving him “in the same state as Getafix”. As the two crazed druids concoct a number of skin-coloring potions, Asterix tries to get Vitalstatistix into good physical shape for the fight, mainly by jogging. Meanwhile, the Romans plan to arrest Ceramix after the fight, lest he thereafter challenge their control of Gaul.