Living alone with his mother on the edge of an ever-encroaching swamp teeming with toxic magic, young Nereus Vestryn has grown up hearing stories about the feral people the ''miasma'' has infected.
So when one morning he finds his mother crawling sickened from the swamp, he has no choice but to summon a mage to help her.
But mages are feared figures, reminders of the ways the swamp can twist people, and her arrival has greater repercussions than Nereus bargained for.
As long-held family secrets are uncovered and an unexpected threat arrives on the doorstep, Nereus must ask himself: what really makes a monster?