Get the mission from the gate guard. You need at least 80% of your Rank Points bar filled to receive this mission.
Speak with Apururu in the Manustery who will explain that her brother is locked in a Dungeon, and only you can save him, by collecting five rings to open the dungeon door. These rings are mostly from past missions - you have to go speak with the NPCs to collect them, as you no longer possess them. Collect the four rings from:
If you spawn the Queen Cardians by clicking the Cracked Wall with Sneak active, they will not aggro. When pulled with a ranged attack or a magic spell, just be at good distance (20'+), they will not link (they will aggro to magic). In this manner, you only need to fight one of the two Cardian; the one that does not aggro will eventually despawn, and you may then click the Cracked Wall again to continue.
They will use their respective 2-hour abilities. For this reason, it is not advisible to attempt to solo the Red Mage.
Can be easily soloed by a Summoner 75 (with Fenrir), while using Spirit Taker on "Easy Prey" mobs around to recover MP. Astral Flow, food & drinks not necessary. It's easier to solo the RDM using this technique.