The one thing that Sullivan, unfortunately, has to admit is that his brother taught his girls well. That combined with their Alpha blood is what has made it so difficult to get rid of them.
From when he got that witch Radagast to try and capture them, they have been slippery as eels, and he still hasn’t figured out how the one that was actually dead, managed to return from the dead!
He has tried almost everything to get rid of them, and it seems that all that remains is to attack Frank straight on when his daughters aren’t around. Take the territory with brute force and then defend it with everything he’s got.
Mia did say that someone was going to die. In his mind, it can only mean Frank’s days are numbered. He walks through the rows of men that he has been gathering to make sure there
