Complex sentence: Catelyn convinces Brienne to escape with her so that she may at least avenge Renly someday; during their journey, Brienne swears allegiance to Catelyn so long as she never interferes with her vengeance on Stannis (Stephen Dillane).
Split into simpler sentences: Catelyn convinces Brienne to escape with her so that she may at least avenge Renly someday. During their journey, Brienne swears allegiance to Catelyn, who promises not to interfere with Brienne's vengeance on Stannis (Stephen Dillane).