Kill the leaders and open the chest in the entrance of the Plains temple if you didn't do so, then kill a war cricket and get inside. You will see 2 Scorpions. Kill them and proceed further into the temple. Choose the path on the left but don't go too far. There is a trap that will crush you into ashes by a huge rock. Use telekinesis to pull the lever and deactivate the trap. Kill a few elite warriors and proceed through the left and kill the Ashbeast you see. Jump across the chasm and climb up to reach a room that contains a High Priest. Use the scroll Destroy Magical Force Field to break the red magic barrier.