Elemental logic, book 1 : Fire logic
Laurie J. Marks2002

In the world of Fire Logic, the rare individuals born with magic talent are known as elementals, because they possess the power of fire, earth, air, or water. The fire elemental Emil is a Paladin, a Shaftali soldier-scholar who is about to embark on his most desired studies when the invading Sainnites capture the capitol and kill the wizard ruler, leaving no heir; now Emil must become a war commander in the remnants of the Shaftali army. Another fire elemental, Zanja na'Tarwein, is the Ashawala'i Speaker, but she cannot convince her own people of the full danger of the Sainnites. Karis, a half-giant blacksmith, has tremendous earth powers that might defeat the Sainnites--if she weren't addicted to a potent, deadly drug that steals her will. Her guardian, Norina the Truthken, is an air elemental able to see through any lie, yet she is blind to dangerous truths about both her half-giant charge and Paladin treachery.