This mission follows after the failed siege at Helms Deep. Because the orcs were outnumbered , they retreat back and head to their home , Isenguad.
Gandalf suspect that Saruman will regroup and attack again the lands of Rohan. To end him for good , he , Theoden , Legolas , Aragorn and Gimli follow the orcs in to the ancient fortress of Fangorn. But , the orcs wont find any place of refuge there. The forest is full of Ents and Elfs that are guarding the ancients trees that live there for hundreds of years.
You are not alone. The Ents are angry , because the orcs cut of many trees , and they will help you.Use all siege equiqments you wil find in the forest. It will help you a lot.
NOTES AND TIPS :
-take out any orc in the forest
-destroy the village outside of Isenguard to stop them cut any trees
-find any troops or siege equiqments in the forest , because you will need them
-the only way to enter in Isenguard courtyard is to destroy the gatehouse
-you will need to destroy the walls too , because archers should fire in your troops
-destroy the dam to release the river into the orcs head :D