Lord Alchemist Duology Series by Elizabeth McCoy

The Lord Alchemist must be immune to hostile potions. But in all the country, there are only two known immunes: Iathor Kymus, the Lord Alchemist, and his feckless brother, Iasen. Kessa is a half-barbarian herb-witch, arrested for crimes she didn't quite intend... moreThe Lord Alchemist must be immune to hostile potions. But in all the country, there are only two known immunes: Iathor Kymus, the Lord Alchemist, and his feckless brother, Iasen. Kessa is a half-barbarian herb-witch, arrested for crimes she didn't quite intend. But when Iathor discovers her immunity to truth potions, he'll do whatever he must to court her -- guilty or not, she's his only hope of banishing his nightmare: a son enslaved to him by the loyalty potion that each Lord Alchemist's heir must drink, and defeat. But Kessa doesn't trust him, Iasen despises her tainted blood, and there's still the mystery of who complicated Kessa's little crime into the bigger one she didn't intend. They don't even have the benefit of lust at first sight. All they have in common is the alchemist's immunity, and an ability to get on each other's nerves. Will it be enough? (Contains mature situations.) less

The Lord Alchemist must be immune to hostile potions. But in all of Cymelia, there are only three with the alchemist's immunity: Iathor, his brother Iasen, and the half-barbarian herb-witch, Kessa. Though Kessa is hardly the expected wife of a noble, Iathor has secured a betrothal - but his brother has vowed to prevent the marriage by any means necessary... moreThe Lord Alchemist must be immune to hostile potions. But in all of Cymelia, there are only three with the alchemist's immunity: Iathor, his brother Iasen, and the half-barbarian herb-witch, Kessa. Though Kessa is hardly the expected wife of a noble, Iathor has secured a betrothal - but his brother has vowed to prevent the marriage by any means necessary. Iathor will do whatever he can to keep his wife, no matter what she's done or what his brother tries, but Kessa's own dark secrets may sabotage any hope of a happy ending. (Herb-Wife is the second in the Lord Alchemist duology, and is the sequel to Herb-Witch. This book contains mature situations.) less