This guide continues the walkthrough for the Side Quest Bolstering the Ranks.
Enter Ruunvald Temple from the Ruunvald Excavation. Proceed through the caves, and arrive at some big throne room. Kill Moric Sidrey and Minorne. These are tough opponents, so watch your health during this battle. Both Minorne and Moric will cast spells at you from above the stairs, so if possible approach them and attack them in melee. There will be some charmed vigilants here also to deal with.
Minorne carries the Staff of Ruunvald, a staff that makes creatures and people up to level 8 not fight for 30 seconds. More importantly, Minorne has the Ruunvald key, a key needed to open the gate to the cage in which Florentius Baenius is in. Make sure to search the room for loot, mostly inside urns near the walls.
Unlock the cage and talk to Florentius Baenius. He is sure that Arkay sent you (Arkay is the god of Birth and Death). He asks what he can do to thank you. Tell him to meet you at Fort Dawnguard, because Isran needs his help. Florentius is upset and asks if this is some kind of joke. Isran did nothing but mock him. Tell him again that his help is needed. He appears to talk to himself, and then agrees to come to Fort Dawnguard, saying that's what Arkay told him to do.
Climb down the stairs and exit through the iron door (requires Ruunvald Key) to the south. Go through the narrow tunnel and open another iron door. There is a table in one of the rooms here with a book on it, "The Aetherium Wars". There are also some useful potions on this table, and an urn nearby. In the east end of the room near the bed there is some chest with valuable items such as a glass shield, dwarven helmet, a sapphire, and a lot of gold. In the south edge of the room there is a lever which you can activate that will open a secret door in the center. Go down the spiral stairs then west up some stairs, unlocking a door to Skyrim with the Ruunvald key.
This completes the quest, Bolstering the Ranks. You may return to Fort Dawnguard for further instructions.