Fire Emblem: The Sacred Stones/Chapter 10: Turning Traitor

Rush down and talk to Duessel with Ephraim and a few cavaliers as soon as possible, or Cormag will get too close to Duessel to recruit Duessel without Cormag battling someone. Having Tana talk to Cormag helps a ton. Kill all the people surrounding Beran, then kill Beran, and you will have won the battle.