D'Artagnan arrives in Paris trying to find his attackers after being left for dead, which leads him to a real war where the future of France is at stake. He aligns himself with Athos, Porthos and Aramis, three musketeers of the King.
A crew of aquatic researchers works to get to safety after an earthquake devastates their subterranean laboratory. But the crew has more than the ocean seabed to fear.
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.