Following a fall during mistletoe picking, Druid Getafix decides that it is time to secure the future of the village. Accompanied by Asterix and Obelix, he undertakes to travel the Gallic world in search of a talented young druid to transmit the Secret of the Magic Potion.

Paris, Montmartre, 1883. Seraphine, 12 years old, leaves a monotoneous life with Jeanne, the grumpy seamstress who raised her. She is obsessed with finding out who her parents were. Flanked with Mistigri, a street child whom she takes under her wing, Séraphine retraces the secret of her origins and finds it in the battles led by the people of Montmartre.