Move down the West Forest and kill off the minor enemies you come across. You'll eventually enter the cavern where Leona is waiting for you. After agreeing to help out, head down deeper into the caves and battle through more mercenary footsoldiers and riflemen.

The cave doesn't have too many surprises, but you will fight a few named mini bosses with strengthened auras and extra minions. These include the archer Barbat that can deal heavy damage, but is slow with his shots.

In the heart of the cave you'll eventually find the mage sister Vera and her underlings. You will be extremely out numbered and only fast reflexes will be enough to survive. Use your dodging, blocking and buffs as much as possible to keep yourself protected. Focus first on the weaker mercenaries, followed by the summoned skeletons. Vera and the other mages can resummon the undead, so be fast at killing the sidekick casters.

This will eventually leave you against only Vera and the few skeletons she can conjure. She uses both a close range wave spell similar to Katarina's Warding Ritual and can launch magic missiles. Keep evading by rolling and hit the mage while she attempts to recast.

Once the witch is dead, loot the area for new equipment and search the caves to find captured Legionnaires. Among them is the young ward Armand who will return back to Odo. More importantly you will find one of the other three heroes. Who is inside depends on your own party member, but the prisoner is likely to be Anjali.