Burning Tower — Larry Niven; Jerry Pournelle

But fires aren't the only danger the residents of Tep's Town are facing. From out of the desert come monsters -- great birds with blades instead of wings. Magical birds, driven by some unknown force for some unknown reason. Although they can be killed, the danger these birds pose is greater than mere death. Without their god, the people of Tep's Town can no longer stand alone. Danger on the roads means no trade. No trade means that Tep's Town will die.

Sent by the Lords of Lordshills to discover the source of the aptly-named terror birds, Lord Sandry and his beloved, Burning Tower, must travel beyond the walls of their home into a world where the manna that fuels magic is still strong -- and someone or some-thing waits to destroy them!