Samuel R. Delany 
Out of the Dead City [EPUB ebook] 

The Empire of Toromon had finally declared war. The attacks on its planes had been nothing compared to the final insult — the kidnapping of the Crown Prince. But how would the members of this civilisation — one of the few that survived the Great Fire — get beyond the deadly radiation barrier, behind which the enemy lay? And assuming they got beyond the barrier, how would they deal with that enemy — the Lord of the Flames — whose very presence was unknown to the people among whom he lived?