This mystery can be found on the eastern coast of Lincolnscire, at Skegi’s Beard.
Speak with Skegi & Stikla and Eliminate the Bandits
As you approach the fishing village of Skegi’s Beard, you’ll see two figures on the cliff edge overlooking it. Both seem to be contemplating the loss of it, and you can find out more by speaking with them. A cutscene will begin during which Skegi explains that the bandits claimed the settlement once they discovered the bountiful fishing opportunities. Skegi no longer has the strength to fight them, but his wife Stikla is younger and keen to take revenge. You can choose to take Stikla with you or eliminate the bandits on your own. Either way you’ll need to defeat every single bandit until Eivor comments that there are no more, at which point you can return to Skegi to complete the mystery.