Mercenary’s March. The Schooled in Magic Universe, #2

Fifteen years ago, the Kingdom of Kentigern was destroyed by a necromancer and his army of orcs, the Royal Family and a handful of aristocrats and commoners forced to flee across the Inner Sea before it was too late. Since then, few have set foot on Kentigern and fewer still have returned, leaving the refugees trapped, unable to return home. But now the Necromantic Wars are over. Determined to keep his vow to return, Crown Prince Hadrian of Kentigern raises an army of mercenaries, armed with the latest weapons and magitech necromancer-killing devices, and sets off to reclaim his father's kingdom.
For Sir James, Captain-General of the Bloody Hands, it is a chance to gain the titles and wealth that should be his by right; for Robin and Eliza, runaways from aristocratic justice, it is a chance to make a new life for themselves, far from their former tormentors. But it won't be as easy as they think, because the ruined kingdom hides a far darker secret than a necromancer, and one far more dangerous .