Escape from Bythos — Phil Tucker

While listed as book 6, Escape from Bythos is actually the prequel novella to the series and can be enjoyed at any point.

How did Asho end up as Lord Kyferin's squire?

Escape from Bythos leads seamlessly into the novel The Path of Flames, detailing how Asho acquired his freedom against all odds and escaped the slave city of Bythos.

All Ennoian knights must sacrifice a single year of their lives to garrison the subterranean city of Bythos. Known as their Black Year, it is a time both loathed and dreaded. Lord Kyferin, the infamous leader of the Black Wolves, is down in the depths with six of his knights. Biding his time. Whoring. Dreaming of bloody invasions he'll launch when he is free to return to Ennoia.

Then a Bythian slave brings word of dangerous prey. A legendary monster. A cavekiller. Kyferin chooses to mount a hunt, taking a fraction of the men needed so as to increase his glory. This cavekiller, however, is different. More lethal. Ferocious. And the Bythian slave that Kyferin brings as a guide is none other than Asho's father....