A briefcase with undisclosed contents – sought by Irish terrorists and the Russian mob – makes its way into criminals' hands. An Irish liaison assembles a squad of mercenaries, or 'ronin', and gives them the thorny task of recovering the case.

Years have passed since the Three Musketeers, Aramis, Athos and Porthos, have fought together with their friend, D'Artagnan. But with the tyrannical King Louis using his power to wreak havoc in the kingdom while his twin brother, Philippe, remains imprisoned, the Musketeers reunite to abduct Louis and replace him with Philippe.