This quest begins immediately after The Sons of Ragnar.
Make your way west of Tamworth Fortress to Tonnastadir, where you can regroup with Sigurd, Ubba and Ivarr. Speak with Sigurd and enter Tonnastadir to speak with Tonna. When Eivor suggests payment for information, you will have the option of paying 520 silver to learn all there is to know and end the quest. If your Charisma level is at least 2, you can insist on 260 silver as payment for the information.
If you’d rather not pay anything at all, there is a third option: sneak into the camp and find evidence of the arrangement between Tonna and King Burgred in the form of a letter, which can be found in the basement of Tonna’s house. To pursue this, just select “I’m not going to pay you.” when speaking with Tonna. After the brief cutscene, you’ll have the opportunity to sneak into the settlement and reach Tonna’s house without being seen. While there, you’ll also have the opportunity to obtain some unique gear and a new ability.
Infiltrating Tonna’s House
From the front gates of Tonnastadir, head north and climb up the rock face. Don’t be tempted to run too much along the wall boundary here. If you make too much noise the guards may be alerted to your presence, making the infiltration a lot more difficult. Remain crouched as you follow the wall northwest toward the longhouse. Just before you reach it, you’ll see an opening in the wall, providing access to the settlement. You’ll benefit from making a hard save here, just in case you blow your cover and need to start over.
Before you enter the settlement, use Odin’s Vision to see the precise location of any troops in the vicinity. When you’re ready, edge along the wall boundary to your left (facing southeast) until you see a gap in the fence. Jump through this into the long grass below. From here you will be unseen, but with a good vantage point of the situation. Use Odin’s Vision to highlight the nearby evidence, and any guards that you may need to take out to access it. While crouched, move through the long grass to the southeast, where you can take out a guard on their own.
With the first guard assassinated, you’ll need to wait for another to come by. There are two guards which patrol around the house, but once they’re dead you will only have to contend with static guards. Kill the second guard as they approach the body of the first, being careful not to give them time to alert the others once they’ve spotted the body. Now that both patrols are dead, you will find only one guard by the entrance to the house. If you followed the above tip, you should only need to assassinate this guard before you enter the house. Otherwise, Tonna will be sleeping inside.
If you want to give yourself a bit of a challenge by infiltrating the house at night, you’ll need to be extremely careful once you’re inside. Any sudden movement will wake Tonna, and it is likely that she will wake up when you attempt to destroy the wooden barricade to the basement below. If this happens, you should run outside back to the area of long grass. If you’re quick enough, Tonna won’t be able to track you and you’ll be able to re-enter the house and climb down the hole without making any noise. In the basement you’ll find the evidence you need in the form of a letter indicating the location of two of King Burgred’s residences, along with some minor treasure.
Unique Gear, Ability, and Minor Treasure
Now that you’ve found the evidence you need, you could go back to Sigurd to complete the quest. However, if you want a little more out of this area, read on.
Exit Tonna’s house the way you came, making use of the long grass as you head west toward the longhouse. Assassinate any guards outside the longhouse, and then make use of Odin’s Vision just before you enter to highlight the location of any guards within. Enter the house while crouching to remain unseen, and take out each guard either with your bow or by careful assassination. With all the guards dead, use the ladder (facing north), then turn right and take the second ladder (facing south) to reach the loft of the longhouse. Here you’ll find the first minor treasure chest. Before you leave, take the key (Tonnastadir Door Key) from a small table at the northern end of the ground floor in the longhouse.
Next, head a short way west from the longhouse. Here you’ll see a small house with the door barred. Kill the guards inside and outside the house to loot the treasure chest within. The third and final piece of minor treasure can be found in a triangular house located south of the one you’re currently in. Step out the front door to see the house to the left of the tower in the distance. This triangular house has a front door which is barred, but you can enter from the back by destroying the wooden barricade, as shown below. Once inside, simply loot the treasure chest and exit from the front door.
With all the minor treasure collected, it’s time to make use of that Tonnastadir Door Key. Head south from the longhouse until you reach the entrance to a hidden passage (shown above), marked by a Secret Entrance icon on your map. Kill the three guards in front of the entrance in whatever way you see fit. An effective method is waiting for one of the guards to move away from the door, providing you with an opportunity to shoot them in the head. You can then kill a second with leap assassination, leaving the third ripe for the picking. Use the key to open the door and follow the shaft north. First you’ll find a chest containing the Huntsman Helm, then through a crack to the east you’ll find a Book of Knowledge which bestows the Raven Distraction ability.
Now that Tonnastadir has been thoroughly looted, report back to Sigurd, Ubba, and Ivarr at Lyftmere’s Pond, located south of Tonnastadir, to complete the quest.