In order to complete this quest you have to finish the 2nd statue of floor 1 first. This will unlock a new area at i2 where you can find the Inoverche Duram. Ask him about Chloe and the hidden passage. You will now need to find that mentioned passage which is located at g6/7 (5x Meat Puppet room). You can't open it yet so head back to Duram and ask him how to enter the hidden passage. Return to it and you will enter a final battle.
Monster: 10x Wasted Life
You will spawn in the middle of the mobs so use your invulnerability to enter either the small hallway or the bigger room next to it. Those mobs are accelerated and as strong as normal Wasted regarding HP, defense and attack.
After completing the final battle there will be a short cutscene and you can turn in the quest.