Greg Rich has traveled through time, become one of the legendary Musketeers, and—most recently— prevented the Spanish army from attacking Paris. He should feel invincible. Instead, he and his friends languish in prison, having stumbled into a trap set by Milady and the Prince of Condé.

But Greg didn't come to the seventeenth century to sit in a jail cell and await execution. He, Aramis, Athos, and Porthos are Musketeers, and King Louis is in immediate danger of being overthrown by the scheming prince. Faster than they can say "All for one, and one for all," the boys plot to break out of prison, defend Louis, and return Greg and his parents to the twenty-first century.

Amid narrow escapes, flying arrows, and fiery explosions, the Musketeers battle to save the king— and history itself. Because if the past changes, what happens to Greg's future?