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

Rush down and talk to duessel with ephraim and a few cavaliers ASAP, 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.