What was done by the sword shall be undone by the sword

Background
''Following the War of Shadows... Princess Shiida of Talys was engaged to Prince Marth of Altea, and all of Talys rejoiced. However, taking advantage of this chance, a clan in the outskirts of Talys suddenly started a rebellion. Having taken only a few bodyguards with her, Princess Shiida was swept away from the city and into the battlefield, her whereabouts unknown... The leader of Talys's hired swords, Ogma, commands his subordinates and immediately marches out to rescue Shiida.''

Chapter Information
What was done by the sword shall be undone by the sword is the third downloadable episode in Fire Emblem: Shin Monshō no Nazo ~Hikari to Kage no Eiyū~.