This quest begins immediately after The Ritual of the Berserker. You will have no time to do anything else, as Bjorn is already charging Beodoricsworth.
Attack Beodoricsworth with Bjorn
This is as simple as it sounds. You will be charging at Beodoricsworth with Bjorn, and your task is to kill any Mercian soldiers that you find there. Most of the soldiers will be regular units which are easily defeated, but you will come across one or two with greater skills such as Yeomen and Spearmen. You’ll need to use heavy attacks to break through the defences of the Yeomen, and you’ll need to make use of dodge and roll to flank the Spearmen effectively, striking them before they can put up a defensive stance. You should be able to strike the Spearmen with a couple of light attacks initially, but they will almost always block your third attack, so you’ll have to mix the flurry of blows up a bit to catch them off guard.
When you first enter Beodoricsworth, you’ll be met by numerous regular enemy units. You can use abilities such as Throwing Axe Fury to damage multiple enemies at once, or use a two-handed weapon for a lot of area of effect damage. Either way, with the help of Bjorn and Njal, you shouldn’t have too much trouble taking out most of the guards here. The most difficult enemy unit you’ll find in Beodoricsworth is a Housecarl, who yields a flail and a seax. In truth, they’re not as difficult as they sound if you have a fast weapon like a bearded axe, since you’ll be able to overwhelm them with a flurry of blows. You’ll only run in to trouble if you hesitate to strike and give the Housecarl time to counter, at which point they can retaliate with damaging strikes. Take them out as quickly as possible and try not to get flanked when they roll on the ground.
Once all the enemies within Beodoricsworth are dead, follow Bjorn to the northwest and leave the area.
Gather Flowers for Njal
Now that Bjorn has finally avenged the death of his wife, his bear Njal is near death. As a final gesture, Bjorn asks Eivor to bring him some of the flowers which can be found near the Gallows Tree. Make your way back to the tree, south of Beodoricsworth, and use your raven to identify the precise location of the flowers. Once you’ve picked them, meet Bjorn and Njal beneath the tree. A cutscene will begin here, and you’ll have a few dialogue options. It doesn’t matter which you choose, the outcome of the quest will be the same.