With Carnan laid low by her previous efforts, the orcs have moved in and begun torching her forest. Obviously this cannot stand. There are four totems to purify, using the same methodology as the previous few missions.
The nearest one is the rightmost one. As usual, knock the guards down or away long enough to complete the purification. Also as usual, a chained stealth kill is a strong opening move in clearing some space.
Give priority to taking down spear throwers if you can- a javelin in the spine can really disrupt your concentration. This is especially true of the last totem. You may consider recruiting or summoning a caragor to help keep them under control.
When the last totem is down, follow your marker back to Carnan. Orcs with torches are trying to set her aflame- mow them down.
The caragor lets you travel swiftly up and down the line, but sprinting on foot usually gives you quicker kill options. Either way, Carnan has enough health that this isn't a very hard fight, just keep moving and mauling until the orcs have been driven off, and you'll get a story marker to join Carnan.
The cutscene here ends the mission.
