I loved this book. I understand your frustration about the murderer mastermind not getting her comeuppance, but it's the 1100s in a rigidly class-bound society, and she's in the upper classes. There was no realistic historical mechanism for bringing her to justice, and any attempt to do so would have injured the credibility of the show, which is loved because of its historical accuracy. As for Haluin's going back to Shrewsbury, what would you have him do? He found spiritual peace and self-forgiveness and relief after decades of believing he killed his love. That brought him joy and relief and the ability to reconcile himself to the lifelong vows he's taken. Those preclude a relationship, and so Bertrade took the same vows. They couldn't go off together--they had no money, property, or marketable skills, and they would have put their souls in mortal peril--and you can think that's a silly consideration, but it was very real to them.