D’Artagnan is forced to join forces with Milady to save Constance, who was kidnapped before his eyes. But as war is declared and Athos, Porthos and Aramis have already joined the front, a secret from the past shatters old alliances.

The only daughter of the Chinese emperor Han Xuandi, escapes from a strict prince and seeks help from the Gauls and the two brave warriors Asterix and Obelix.