"Yngvarr has kidnapped Agnar's wife and son. We must head to Fort Urokk to get them back before Yngvarr does something to them."
This quest has two very dangerous parts where your group will be seriously outnumbered by bandits in an area with little cover from them. None of your companions can be killed, which is fortunate as protecting them would be impossible, but you can, so be certain to stock up on any necessary healing and replenishment potions and spell scrolls.
Speak to the Jarl and he tells you that the exit door is locked and the only key they have doesn't open it. He asks you to go to the upper levels and gives you the Fort Urokk Upper Levels Key.
"We've found Jalma and Wilhard alive and have freed them. Our way is blocked, so while Ulgar and Svegard try to get passed the door, Agnar has asked me to search the rest of the keep. I should be careful, I don't know what I'll find."
At the end of a passage just to the east of the cell is a door which can only be opened with that key. Open it and go through. There are three bandits in the next room; these are close enough that the others may be drawn into battle with them. Continue heading upwards, encountering more bandits along the way, climbing the stairs until you reach the top of the tower.
A ladder leads to the exterior here. There is a circular enclosed area with only the trapdoor used to reach it as an exit. An Orc called Kolgrim will threaten you, say that you will never get the key, and then attack, even if you are sneaking. This opponent may be a bit tough. Once he is dead, search the body for the Key of Shelter and take it, then go back into the fort and return to Agnar.
Speak to Agnar, and he asks if you found anything, because they managed to open the door in your absence. When he hears that you defeated Lieutenant Kolgrim, he takes the Key of Shelter from you, and says that now the fort is without a commander you should kill as many of the soldiers as possible.
"Kolgrim is dead, and the fort is in dismay. Agnar has decided to take this chance to reduce the size of Yngvarr's army. We are going to kill all the troops he has here before leaving."
Go through the wooden door and follow them into the exterior areas of the fort, where there are a 24 bandits waiting, although not all of them are immediately outside the door, enough to easily overwhelm you, especially as they seem able to detect you even if you are sneaking. A save is a good idea at this point.
Make sure you exit at the same time as everyone else, otherwise you may find yourself all alone and the rest of your, unkillable, companions too far away to help. Once all the bandits are dead, you need to open the main gate. The lever that opens it is located in the tower to the east of the gate. Pull it, then make your way down and exit through the, now open, gate. As you do so, Yngvarr approaches with some troops in a cutscene.
Yngvarr demands that Agnar gives him the keys. Agnar says he wants his friends to be left alone. Yngvarr says that he will let the others go, but not Agnar, if he is given the keys. Despite the others urging him not to, Agnar gives Yngvarr the keys. Yngvarr then leaves and orders his troops to kill everyone. You will now be in a dangerous battle with 14 Elite Guards, 8 melee and 6 missile, who seriously outnumber you.
"Yngvarr approached the fort just as we were leaving. He had a great many troops with him. Agnar exchanged the keys with him in return for our lives. Yngvarr did not keep to his word and ordered us all killed. We must now killed off his guards."
Once all the guards are dead, you need to approach Agnar. He says that with all the keys, if Yngvarr gets his hands on the Heart of the Gods, it will make him immortal. He asks you to meet him back in Amber Creek, whilst the others will come up with a plan along the way.
"We found Agnar's family, but we lost all of the keys. Yngvarr is now very dangerous. We must plan what we are going to do next."
Make your way back to Amber Creek. You may have to wait there until Agnar arrives. Once he does, speak to him and ask him what the plan is. He says that he is raising an army, and that they are going to siege Staalgarde. You and Ulgar are going to clear a way through the valley. Agnar asks you to go and meet Ulgar, who is waiting with some soldiers at the Emerald Valley Gates. He also says that, once camp is made, no-one will be leaving, so make sure that you are ready before agreeing to continue when speaking to Ulgar after clearing the way. In other words, take everything that you may need now, as you won't have a chance to get it later.
"I need to prepare to siege Staalgarde, and when I am ready I must meet Ulgar at the base of the hill leading up to the Emerald Valley Gates."
Go to where Ulgar is waiting with three Amber Creek Soldiers, then follow him up the hill to the Emerald Valley Gates. This is yet another battle in the open where you are outnumbered by seven soldiers, only this time, Ulgar is the only one of your companions who cannot be killed. Once the gates are cleared, follow Ulgar - and anyone else, if they are still alive - further up the hill to where there is a small camp just before some gates with some more soldiers in front of it. Once they are dead, speak to Ulgar and he will ask if you are ready. This is your last chance to prepare before the battle, so make sure that you are.
Once you agree, there will be a cutscene where Agnar is addressing the troops. Next to you is Olvir, who met you in An Ancient Gate. Ulgar asks for everyone's attention, then Jarl Agnar gives a speech about just how really bad Yngvarr is. Once he has finished, the battle commences. Proceed to the city, which is being bombarded by catapults. There are a few Staalgarde Soldiers outside, but many more inside. Make your way to Unnvaldr Keep, which is easy enough to find by following the rest. Along the way are many enemy soldiers; you initially start with many friendlies too, but by the time the keep is reached, these will likely all be dead. At a courtyard with some horses in it, everyone waits.
Before entering, save the game. Once inside, you cannot leave until Agnar has finished his speech after the guards are defeated, and sometimes the doors don't work. Open the door and enter Unnvaldr Keep. Only Agnar will accompany you inside. Inside, Yngvarr is waiting with four Elite Guards. He has a nice gloat about how he is going to the Heart of the Gods, and how he didn't originally know where it was, until he had the book stolen whilst everyone was rescuing Jalma and Wilhard. He then leaves, and the four guards attack. You will need to kill them all in order to exit. To the left of the entrance is some debris, which can be jumped behind. Against the wall, there, the guards will be unable to reach you if you are standing far enough back, but you can still cast spells and use a bow. Once all four are dead, the quest is complete.
"Yngvarr escaped and sent his elite guard to kill me and Agnar. We fought them off, but Yngvarr had gotten away. We need to chase him to the Heart Chamber."
The main quest series concludes in The Heart of the Gods.