Rostam fighting the demon Arzhang and Arzhang's army.
Taking care to secure his hostage, Rostam waltzes up to demon camp and attacks.
... and when the sun rose he used his lariat to tie Olad tightly to a tree. Then he hung his grandfather's mace from his saddle and rode into Mazanderan, his heart filled with schemes of conquest. He wore a royal helmet on his head, and his cuirass of tiger skin was soon soaked with sweat. He set off to find Arzhang, and when he came on the demon's army he gave a great cry that seemed to split the sea and mountains. Arzhang heard this shout and came rushing out of his tent: Rostam saw him and urged his horse forward, bearing down on him like fire.
Yeah, it doesn't end well for the demon Arzhang, who along with his rest of the army is soon dead. Kay Kavus and the hostages are free!
But he has to go and kill the White Devil now, because not only is the White Devil the leader of all the demons, but his blood will cure Kay Kavus' blindness.