From the bridge of the submarine Sea Serpent, Lt. William Kenlon saw a huge creature flying overhead with a wingspread unlike that of any bird the young naval officer had ever seen. 

Almost instantly it disappeared, and Kenlon thought the strange bird had been only an apparition.

Suddenly, it reappeared, and Kenlon found himself fighting for his life in the cold water of the night. As he finally surfaced it was to find himself at the beginning of a journey into a fearful future where a grotesque war was being waged between the frightening birdmen and their even more terrifying opponents. ...