Keepers of the Flame by Robin D. Owens

As Owens' multifaceted saga, The Summoning, continues, the sorcerers get an unexpected bonus: two for the price of one in the form of twins...Events continue to darken in this intricate fantasy world, the stakes keep rising, and losses become inevitable. Strong characterization combined with deadly danger make this story vibrate with emotional resonance. Stay tuned as events accelerate toward the final battle.

Twin sisters Bri and Elizabeth Drystan each have a special gift for healing, but they've taken very different career paths. While Elizabeth has pursued a medical degree, Bri has taken a more unorthodox and holistic path. Both of their gifts are sorely needed in the world of Lladrana, as the Dark has launched a deadly new plague.