After defeating Rikywulf and returning to Fornburg, you will meet Sigurd. He introduces you to the Invisibles and you gain access to the Hidden Blade. After this quest, Kyotve sends his spies to collect information about Eyvor and his people. Eyvor notices the scouts and sets out to kill them all.
Removing the first spy is pretty straightforward. His location is marked on the screen and all you have to do is chase him and then get close to him. Once he gets close enough, you just need to kill him, which will complete the first part of the quest. But the second part of the task requires you to find the remaining spies in Fornburg.
To do this, you need to return to Fornburg after defeating the first spy. The quest marker will appear on the map, but as soon as you get a little closer to it, it will simply disappear and give you no information about the exact location of the spies.
To find enemies, you need to use a raven. You can do this by entering Raven Mode and exploring the area. The area where the spies are hiding will be highlighted in green. It is located far from Fornburg, in a hilly area. You will see a camp with a bonfire surrounded by hills – it is in this place that the remaining spies are hiding.
Mark the area with a marker to make it easier to find it after exiting Raven Mode. Once you reach the place, simply eliminate all opponents. You will also find a note from Kyotve in the camp, in which his spies ask about the power of Eyvor and his people. Once you complete the task, simply return to Fornburg and interact with Sigurd to complete the quest completely.