Dahut

In book three of the King of Ys series, Gratillonius's reign faces a deadly new threat from across the sea
For sixteen years Gratillonius has been the king of Ys, a position he has used to bring the once-teetering city-state back to stability as the Roman Empire continues to collapse around it. Rome would prefer a more malleable leader in Gratillonius's place and makes no secret of it. As pressure from Roman leadership increases, Gratillonius must also contend with Niall maqq Echach, the leader of Northern Ireland who holds the Ysan king responsible for the death of his son. Compounding these complications is the ever-present threat of retribution by the Ysan gods, should the kingdom's leadership make a misstep. But perhaps the greatest danger of all is unfolding from within Gratillonius's own household, where, following the death of one of his nine wives, the gods have named an unsettling replacement: Dahut, Gratillonius's own daughter.
As treachery...